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Simulation of the regional atmospheric transport and fate of mercury using a comprehensive Eulerian model
Abstract
This paper describes the development, testing and evaluation of a comprehensive mercury simulation model. The model was developed by starting with an existing model that simulates the sulfur/NOx/VOC system and then substituting modules specific to mercury (e.g. chemistry and scavenging). The transport and fate of mercury emissions in the contiguous United States was simulated with the mercury simulation model. We first tested the model by simulating the sulfur system using emissions from the 1990 U.S. EPA criteria pollutants inventory. This testing provided a measure of the uncertainties in the meteorological input data (e.g. gridded wind, cloud and precipitation fields) and model parameterizations (e.g. transport:) that are common to both the sulfur and mercury systems. The mercury simulation model was then evaluated by comparing model estimates of annual average concentrations and wet deposition amounts of mercury against published measurement data. The mercury evaluation showed that the model captured the range of observed values in most regions where observations were available. Moreover, observed spatial gradients in mercury wet deposition amounts and ambient concentrations were also seen in the model results. For the scenario considered here, the simulation results lead to an annual mercury wet deposition amount that is roughly twice the estimated annual dry deposition amount, for most regions of the modeling domain.
... [1999] and J. Bartnicki [1998] assumed that Hg part behaviour was similar to that of leadcarrying particles. P. Pai et al. [1997] accepted log-normal distribution of mercury-bearing particles and obtained spectrum split into 15 intervals, taking into account gravitational settling as well. For every interval dry deposition velocity was calculated using resistanceanalogy scheme [Pleim et al., 1984]. ...
... The authors noted that the discrepancy could be connected both with possible analytical errors and with unreliable emission estimate for this zinc smelter. P. Pai et al. [1997] undertook calculations of mercury concentrations and deposition fluxes over the USA by TEAM (Trace Element Analysis Model) model. Spatial resolution of the model was 100 km and time step was 1 hour. ...
... Concentrations of a pollutant at a receptor point formed by contributions of all sources are determined by probability of transport from different wind sectors. Eulerian-type models operate on fixed grid and deal with fluxes from one grid cell to another [e.g., Petersen et al., 1990;Pai et al., 1997;Bartnicki et al., 1993;Bartnicki, 1998]. Eulerian-type models can adopt more complicated description of diffusion and chemical transformation. ...
A.Ryaboshapko, Meteorological Synthesizing Center EAST (Russia) 1. INTRODUCTION During the last 2-3 decades considerable attention has been given to problems concerning negative effects of heavy metals (HMs) on various ecosystems in different environmental media. Numerous field observations indicate a significant increase of HM concentrations in agricultural and forest soils as well as in marine and inland water sediments. This increase is frequently observed in remote areas thousands of kilometers away from major anthropogenic sources and can be explained by transboundary atmospheric long-range transport only. An assessment of the potential ecological and health risks associated with atmospheric fluxes of heavy metals requires an understanding of the relationships between sources of emission to the atmosphere and the levels of concentrations measured in ambient air and precipitation However, the complexity of the atmospheric processes of heavy metals makes results from measurement programs difficult to interpret without a clear conceptual model of the workings of the atmosphere. Further, measurements alone cannot be used directly by policy-makers to form balanced and cost-effective strategies for dealing with this problem; an understanding of individual processes within the atmosphere does not automatically imply an understanding of the entire system. A complete picture of individual heavy metal processes and their interactions with the atmospheric system as a whole can only be obtained by means of numerical modeling. A detailed review of existing models of HM regional atmospheric transport was presented at each of the three previous WMO/EMEP workshops on POPs and HMs [Petersen 1993, 1994, 1996]. Since then, new and existing models for long-range transport of HMs have been developed and improved, respectively, with special emphasis on mercury, lead and cadmium, which have been defined by the recently ratified UN-ECE protocol on HMS and POPs to be the priority HMs of concern. The main focus of this paper is on basic features of new model developments since 1996 and on improvements that are still needed to address effectively the issues facing the above mentioned protocol.
... Modelers use descriptive statistics (mean, median, percentile, and standard deviation etc.) to describe the data in quantitative terms. They address correlations using Pearson's correlation coefficient, r (Bullock and Brehme 2002;Gbor et al. 2007;Gbor et al. 2006;Pan et al. 2007;Ryaboshapko et al. 2007a; and coefficient of determination, r 2 (Bullock Jr et al. 2007;Bullock et al. 2009;Kemball-Cook et al. 2004;Pai et al. 1997;Schmolke and Petersen 2003;Yarwood et al. 2003 Also other parameters were used to evaluate model results including percentage of data points that fit within factor of 2 (Pai et al. 1997;Petersen et al. 2001;Ryaboshapko et al. 2007a), index of agreement (Hedgecock et al. 2005;Lin and Tao 2003), as well as, bias and error terms (Bullock et al. 2009;Kemball-Cook et al. 2004;Lin and Tao 2003;Ryaboshapko et al. 2007b;Seigneur et al. 2001;Seigneur et al. 2003a;Seigneur et al. 2003b;Seigneur et al. 2004aSeigneur et al. , 2004bVijayaraghavan et al. 2008;Xu et al. 2000;Yarwood et al. 2003;Zagar et al. 2007). ...
... Modelers use descriptive statistics (mean, median, percentile, and standard deviation etc.) to describe the data in quantitative terms. They address correlations using Pearson's correlation coefficient, r (Bullock and Brehme 2002;Gbor et al. 2007;Gbor et al. 2006;Pan et al. 2007;Ryaboshapko et al. 2007a; and coefficient of determination, r 2 (Bullock Jr et al. 2007;Bullock et al. 2009;Kemball-Cook et al. 2004;Pai et al. 1997;Schmolke and Petersen 2003;Yarwood et al. 2003 Also other parameters were used to evaluate model results including percentage of data points that fit within factor of 2 (Pai et al. 1997;Petersen et al. 2001;Ryaboshapko et al. 2007a), index of agreement (Hedgecock et al. 2005;Lin and Tao 2003), as well as, bias and error terms (Bullock et al. 2009;Kemball-Cook et al. 2004;Lin and Tao 2003;Ryaboshapko et al. 2007b;Seigneur et al. 2001;Seigneur et al. 2003a;Seigneur et al. 2003b;Seigneur et al. 2004aSeigneur et al. , 2004bVijayaraghavan et al. 2008;Xu et al. 2000;Yarwood et al. 2003;Zagar et al. 2007). ...
... Several graphical methods are, in addition, helpful to quantify model performance. Most common methods used by atmospheric mercury modelers include scatter plot (Bullock and Brehme 2002;Gbor et al. 2007;Gbor et al. 2006;Han et al. 2008;Kemball-Cook et al. 2004;Lin et al. 2007;Lin and Tao 2003;Pai et al. 1997;Petersen et al. 2001;Pongprueksa et al. 2008;Schmolke and Petersen 2003;Seigneur et al. 2001;Seigneur et al. 2003a;Seigneur et al. 2003b;Seigneur et al. 2004aSeigneur et al. , 2004bVijayaraghavan et al. 2008;Yarwood et al. 2003;Zagar et al. 2007), time series plot (Dastoor et al. 2008;Dastoor and Larocque 2004;Gbor et al. 2007;Gbor et al. 2006;Hedgecock et al. 2005;Petersen et al. 2001;Petersen et al. 1995;Ryaboshapko et al. 2007a;Selin et al. 2007;, and box plot (Dastoor et al. 2008;Lin et al. 2007;Pongprueksa et al. 2008;Schmolke and Petersen 2003). Other illustration methods such as range plot with capped spikes (Cohen et al. 2004;Shia et al. 1999) has also been used by some modelers but not as extensively. ...
1 INTRODUCTION Atmospheric mercury (Hg) models can be evaluated by comparison of their simulation results with corresponding observation data. In the past decade, modelers used simple statistics to evaluate model performance (mostly atmospheric mercury concentration and wet deposition) (Bergan et al. 1999; Bergan and Rodhe 2001; Bullock 2000; Cohen et al.
... the major input data and output information. This multimedia modeling approach includes: (1) modeling of the atmospheric fate and tranport (including deposition to the surface) with the Trace Element Atmospheric Model (TEAM) (Pai et al., 1997), (2) modeling of watershed and aquatic fate and transport processes with the Regional Mercury Cycling Model (R-MCM) (Harris et al., 1996), and (3) simulation of the uptake of Hg by a piscivorous bird and a piscivorous mammal with a simple terrestrial food web model. This modeling system is used to calculate the potential risk to each animal species due to ingestion of fish, expressed as a hazard quotient (HQ). ...
... In this study, we include a treatment of both input uncertainties and variability. Uncertainties due to model formulation are best addressed through comparison of modeled and measured values (e.g., Pai et al., 1997;Seigneur et al., 1997b) or through comparison of various model formulations (e.g., Hill and Hoover, 1997) and were not included in this study. ...
... The long-range fate and transport of Hg emissions in the atmosphere is simulated with TEAM (Pai et al., 1997). TEAM is a three-dimensional Eulerian model, based on a fixed grid domain that encompasses the continental United States, Canada, and Mexico. ...
We investigate the uncertainties associated with modeling the potential health effects on piscivorous animals of mercury released to the atmosphere. The multimedia modeling system combines an atmospheric fate and transport model, an aquatic cycling model, and a terrestrial food web model. First, the modeling system is used to calculate point values of the animals' hazard quotients (i.e., measures of toxic dose). Next, we use a simplified version of the modeling system to conduct a probabilistic analysis for the Great Lakes region that takes into account input uncertainty, variability, and uncertainty and variability combined. The use of two different software packages for the combined uncertainty/variability analysis led to similar results except for high values (>90th percentile) where some differences were evident. A sensitivity study was performed on the combined uncertainty and variability analysis. Regional variability caused more than 70% of the variance in the results, with the fish bioaccumulation factor accounting for the majority of the variability. The major sources of uncertainty were the speciation of the mercury emissions, the lake pH, and the sediment burial rate.
... Related to FAMS was the Aquatic Cycling of Mercury in the Everglades (ACME) project aiming to study the hydrological, biological, and geochemical processes governing Hg cycling in the Florida Everglades (Krabbenhoft et al., 1998). Important results from these Hg-based studies in Florida included quantification of wet and dry deposition of Hg around Florida and improving models treating the transport and life cycle of Hg (Pai et al., 1997). Long-range transport of reactive gaseous Hg in conjunction with strong convection and thunderstorms during the summer was suggested to account for over half of Hg deposition over southern Florida, with local emissions being less influential (Guentzel et al., 2001). ...
... The FAMS investigation was a coordinated effort over Florida to examine both dry and wet deposition of Hg, but also other species such as sea salt, dust, urban pollution, and acidic aerosols . Pai et al. (1997) reported based on model simulations that the wet deposition of Hg was twice that of dry deposition. The dry deposition of N-containing pollution has been of special interest for the Chesapeake Bay estuary and WNAO coastline as it is a major source of N (Loughner et al., 2016). ...
Decades of atmospheric research have focused on the Western North Atlantic Ocean (WNAO) region because of its unique location that offers accessibility for airborne and ship measurements, gradients in important atmospheric parameters, and a range of meteorological regimes leading to diverse conditions that are poorly understood. This work reviews these scientific investigations for the WNAO region, including the East Coast of North America and the island of Bermuda. Over 50 field campaigns and long‐term monitoring programs, in addition to 715 peer‐reviewed publications between 1946 and 2019, have provided a firm foundation of knowledge for these areas. Of particular importance in this region has been extensive work at the island of Bermuda that is host to important time series records of oceanic and atmospheric variables. Our review categorizes WNAO atmospheric research into eight major categories, with some studies fitting into multiple categories (relative %): aerosols (25%); gases (24%); development/validation of techniques, models, and retrievals (18%); meteorology and transport (9%); air‐sea interactions (8%); clouds/storms (8%); atmospheric deposition (7%); and aerosol‐cloud interactions (2%). Recommendations for future research are provided in the categories highlighted above.
... Air pollution monitoring is thus becoming more and more significant. Real-time air quality information, such as the concentration of PM 2.5 , PM 10 and NO 2 , is an important aspect for pollution management and protecting human beings from damages caused by air pollutants. Considering the significance of air quality, governments take measures to monitor it through establishing air quality monitoring . ...
... In the past decades, many studies on air quality inference have been done using approaches such as dispersion models, satellite remote sensing and wireless sensor networks. Air pollution dispersion models are tools that use a mathematical model such as the Box model [7], Gaussian model [8], Lagrangian model [9], Eularian model [10], SLAB model [11] or some mixed models. to simulate how air pollution disperses in the atmosphere. ...
Air quality information such as the concentration of PM2.5 is of great significance for human health and city management. It affects the way of traveling, urban planning, government policies and so on. However, in major cities there is typically only a limited number of air quality monitoring stations. In the meantime, air quality varies in the urban areas and there can be large differences, even between closely neighboring regions. In this paper, a random forest approach for predicting air quality (RAQ) is proposed for urban sensing systems. The data generated by urban sensing includes meteorology data, road information, real-time traffic status and point of interest (POI) distribution. The random forest algorithm is exploited for data training and prediction. The performance of RAQ is evaluated with real city data. Compared with three other algorithms, this approach achieves better prediction precision. Exciting results are observed from the experiments that the air quality can be inferred with amazingly high accuracy from the data which are obtained from urban sensing.
... The RGM/Hg(II) and Hg(p) concentrations in air are dependent on direct emissions from local and regional sources and on in situ formation in the atmosphere. In the latter cases, RGM/Hg(II) is formed by the oxidation of Hg(0) by O 3 and OH radicals in the gas and/or aqueous phases (Pai et al., 1997;Schroeder and Munthe, 1998). In addition, Sakata and Marumoto (2002) reported that the formation of Hg (p) in the Tokyo metropolitan area might be governed by the physical adsorption equilibrium of Hg(0) between the gas and particle phases. ...
... Conversely, nearly 1% (for observed data) and 9% (for predicting data) of the variance of mercury wet deposition should be due to the local and regional sources of Hg(p) and RGM/Hg(II). This is probably because the mercury wet deposition is dominated by the scavenging of RGM/Hg(II) by precipitation via Hg 0 oxidation by O 3 and other oxidants in the gas and aqueous phases (Pai et al., 1997;Schroeder and Munthe, 1998;Shia et al., 1999). The highest flux (13.2 μg m -2 yr -1 ) was observed at this site, which is strongly dominated by downwind of heavily industrial and urban areas. ...
Air pollution modeling is a numerical tool used to describe the causal relationship between emissions, meteorology, atmospheric concentrations, deposition, and other factors. Air pollution measurements give important, quantitative information about ambient concentrations and deposition, but they can only describe air quality at specific locations and times, without giving clear guidance on the identification of the causes of the air quality problem. Air pollution modeling, instead, can give a more complete deterministic escription of the air quality problem, including an analysis of factors and causes (emission sources, meteorological processes, and physical and chemical changes), and some guidance on the implementation of mitigation measures. In this study we analyze and propose a number of methods, both implicit and explicit, suitable for the task. A theoretical analysis of the proposed methods is given. Optimal methods are identified via a large number of numerical experiments. A set of test problems representative for the application is put together and coded for this purpose.
The Air Quality Management Division of Ministry of the Environment in Japan selected the annual mean environmental air quality standard for hazardous toxic chemicals. The yearly average emissions of mercury from two nearest elevated point sources with background concentration and one-year meteorological data, have been used to predict the ground level atmospheric mercury concentration by atmospheric dispersion modeling. To estimate the mercury concentration in the air of the local area, different models have been used. The first, is AIST-ADMER model that estimates regional atmospheric concentration distribution. The second is METI-LIS model that estimates the atmospheric concentration distribution in the air vicinity of industrial facilities. The third is the Hybrid Single Particle Lagrangian Integrated trajectory Model (HYSPLIT) that estimates the atmospheric concentration distribution in the large domain of coal combustion industrial facilities.
The fourth is the fully coupled WRF/Chem (Weather Research and Forecasting/Chemistry) model is used to simulate air quality over coastal areas of the Sea of Japan. WRF-Chem is the Weather Research and Forecasting (WRF) model coupled with Chemistry. The model simulates the emission, transport, mixing, and chemical transformation of trace gases and aerosols simultaneously with the meteorology. The model is used for investigation of regional-scale air quality, field program analysis, and cloud-scale interactions between clouds and chemistry.
The anthropogenic surface emissions database used as input for this model was based primarily on global hourly emissions data. Despite the low resolution of global emissions and the weak density of the local point emissions, it was found that the WRF/Chem model simulates the diurnal variation of the chemical species concentrations over the coastal areas of the Sea of Japan quite well. However, the back trajectory analysis of HYSPLIT model was also applied in this research to find out the location of sources of pollutants. The Air Quality Management Division of the Ministry of the Environment in Japan selected the maximum level of the air quality standard for ozone, which is 60 ppb. In this study, the atmospheric concentrations of ozone over the coastal area of the Sea of Japan were calculated to be 30-55 ppb during the simulation period, which was lower than the Japanese air quality standard for ozone.
... All the latter contributions are computed according to the Wesely's formula as modified by Walmsley and Weseley (1996). As for Pai et al. (1997), the deposition properties of Hg(II) have been assumed similar with HNO 3 (whose properties are reported in Wesely (1989)), because HgCl 2 and HNO 3 have a similar solubility. Over water, the canopy resistance R c is assumed to be zero because of the high Henry's law constant of Hg(II). ...
... In this study, total wet deposition fluxes were calculated to be 14.3 μg m −2 year −1 , whereas the observed value was 13.6 μg m −2 year −1 at this site. Due to the influence of chemistry and scavenging process of Hg(II) by precipitation via Hg(0) oxidation by O 3 and other oxidants in the gas and aqueous phases (Pai et al. 1997;Schroeder and Munthe 1998;Shia et al. 1999), 1-9 % of wet deposition was not solely explained by precipitation. It should be noted that both cases ( Fig. 7a and b) of the monthly precipitation amount was taken from the AMeDAS observation. ...
Since mercury monitoring activities are very limited in Japan and governmental monitoring data of mercury deposition fluxes are not available, it is necessary to choose some numerical models to protect and manage the local ambient air quality. Numerical models for mercury transportation and deposition should be developed to understand the scenario and pathway of atmospheric mercury concentration distributions and deposition fluxes in the local area of Japan. The ground-level mercury concentrations have to meet the environmental standards set by the Ministry of the Environment in Japan which is less than 40 mg m−3. The aim and scope of this research is to apply numerical models to forecast seasonal variation of ambient mercury concentrations and deposition fluxes in the local area of Japan. To estimate the ambient mercury concentrations in the local area, a dispersion model has been used, the National Institute of Advanced Science and Technology-Atmospheric Dispersion Model for Exposure and Risk Assessment (AIST-ADMER). The AIST-ADMER model calculated the yearly average concentration distributions of mercury in the Aichi Prefecture Japan, which serve as boundary and background concentrations of mercury for the mercury deposition model. Finally, the boundary and background concentrations of mercury calculated by the AIST-ADMER along with meteorological data were superposed in the mercury deposition model to calculate mercury deposition fluxes (dry and wet) in Isshiki Town of Aichi Prefecture. Maximum atmospheric concentrations of mercury were calculated as 2.89 ng m−3 by the AIST-ADMER model. In this study, total dry deposition fluxes and wet deposition fluxes were calculated to be 15.1 μg m−2 year−1 and 14.3 μg g m−2 year−1, respectively.
... Elemental mercury (Hg 0 ) is known having an atmospheric residence time of 0.5-2 years, divalent gaseous mercury (Hg 2 ) remains in the atmosphere for a few hours or days, while for particulate mercury (Hg P ) residence time is a few weeks (Lindqvist and Rodhe, 1985;Schroeder and Munthe, 1998). Over the past years several studies have been conducted to describe the behaviour of mercury released into the atmosphere using mathematical models (Pai et al., 1997;Petersen et al., 1998;Xu et al., 2000;Seigneur et al., 2001;Travnikov and Ryaboshapko, 2002). ...
... Thus the deposition velocity of Hg P is obtained as a weighted average of the previous velocities. The deposition velocities calculated for Hg 2 and Hg P are close to the ones considered by Pai et al. (1997) and Shannon and Voldner (1995). The range of the deposition velocities is 0.1-1 cm s À1 for Hg 2 and 0.02-0.2 ...
Using the well-known Regional Atmospheric Modelling System (RAMS) version 4.3 an integrated system able to simulate the atmospheric mercury cycle has been developed. Basic processes of the mercury atmospheric cycle have been incorporated into the atmospheric model. The model deals with elemental Hg (Hg0), divalent gaseous Hg (Hg2) and particulate Hg (HgP). Wet deposition mechanisms used to describe the removal of Hg2 and HgP are merged with the detailed cloud microphysical scheme in order to provide better representation of the wet deposition processes. The advantages of this approach have been examined through results intercomparison with simulated Hg wet deposition using CMAQ-Hg from previous work for two evaluation periods: 4 April–2 May 1995, and 20 June–18 July 1995. An attempt to clarify the main parameters that affect wet deposition mechanism of mercury is also made.
... This network provides useful information on the spatial and temporal variability of mercury wet deposition in the eastern United States. It has been used extensively for the performance evaluation of mercury atmospheric deposition models (e.g., Pai et al., 1997;Bullock et al., 1997;Seigneur et al., 2001aSeigneur et al., , 2003aSeigneur et al., , 2003bBullock and Brehme, 2002). We are using the MDN database here to develop some understanding of the spatial and temporal patterns in mercury wet deposition. ...
... Because its solubility is comparable to that of nitric acid (HNO 3 ), most models of the atmospheric fate and transport of mercury assume that Hg(II) species have the same dry deposition velocity as HNO 3 . For example, a continental simulation over North America showed a mean dry deposition velocity of Hg(II) over agricultural lands of 0.38 cm s -1 (Pai et al., 1997). Additional experimental data on Hg(II) dry deposition are needed in order to develop a better understanding of its dry deposition process and to remove the assumption that it behaves as HNO 3 . ...
... Therefore, a large amount of work has been carried out to construct, evaluate, and apply mathematical models of the atmospheric fate and transport of Hg. In particular, several models have been applied to Hg deposition in North America (Pai et al. 1997; Xu et al. 2000; Bullock and Brehme 2002; Lin and Tao 2003; Cohen et al. 2004; Seigneur et al. 2004). Model simulations to date have focused mostly on Hg with other pollutants being input to the model as reactants with predetermined concentrations. ...
... te deposition (e.g., Karamchandani et al. 2002). Thus, evaluating CMAQ-MADRID for sulfate allows us to perform a more comprehensive performance evaluation than is possible for mercury because the NADP's Mercury Deposition Network (MDN; NADP-MDN 2006) is less dense spatially than the sulfate NADP network and has been in operation for a shorter time. Pai et al. (1997) used a similar twostep approach in their evaluation of the Trace Element Analysis Model (TEAM). Thus, we first evaluate CMAQ-MADRID for sulfate wet deposition. Next, we evaluate the model for mercury wet deposition. The ability of the model to reproduce the spatial patterns of atmospheric deposition observed in the NADP is then analyzed ...
A multipollutant model, the Community Multiscale Air Quality model paired with the Model of Aerosol Dynamics, Reaction, Ionization, and Dissolution (CMAQ-MADRID), is extended to include a comprehensive treatment of mercury processes and is applied to the simulation of the atmospheric deposition of sulfate and mercury over the United States during 1996. Model performance is evaluated first by comparison with annual sulfate wet deposition data from the National Atmospheric Deposition Program's National Trends Network; the coefficient of determination r(2) is 0.77, and the model normalized error and bias are 53% and -8%, respectively. When actual precipitation data are used to scale the deposition fluxes, r(2) improves to 0.91 and the error and bias change to 42% and -41%, respectively. The scaled results underscore a tendency of the model to underestimate sulfate wet deposition. Model performance for mercury wet deposition is then evaluated by comparison with data from the Mercury Deposition Network. For annual mercury wet deposition, r(2) is 0.28 and the normalized error and bias are 81% and 73%, respectively, when the modeled precipitation data are used. Model performance improves when actual precipitation data are used to scale deposition fluxes: r(2) increases to 0.41 and the error and bias decrease to 40% and 29%, respectively. The model reproduces the spatial pattern of sulfate wet deposition adequately with an increasing gradient from the upper Midwest to the Northeast, that is, from upwind to downwind of large sulfur dioxide sources in the Ohio River Valley. However, the model tends to overestimate mercury wet deposition in the Northeast downwind of these sources that also emit significant amounts of mercury. This "Pennsylvania anomaly" may be due to a partial misrepresentation of the mercury reduction-oxidation cycle, uncertainties in the dry deposition of divalent gaseous mercury Hg-II, incorrect speciation of mercury emissions, and/or uncharacterized emissions in the upper Midwest.
... Physical-based models are based on computational fluid dynamics and chemical reactions. Research was conducted based on pollutant emissions such as fuel consumption, transportation, etc. [1], [2], [3], [4]. Air pollution forecast was conducted based on certain theoretical hypotheses. ...
Poor air quality has become an increasingly critical challenge for many metropolitan cities, which carries many catastrophicphysical and mental consequences on human health and quality of life. However, accurately monitoring and forecasting air qualityremains a highly challenging endeavour. Limited by geographically sparse data, traditional statistical models and newly emergingdata-driven methods of air quality forecasting mainly focused on the temporal correlation between the historical temporal datasets of airpollutants. However, in reality, both distribution and dispersion of air pollutants are highly location-dependant. In this paper, we proposea novel hybrid deep learning model that combines Convolutional Neural Networks (CNN) and Long Short Term Memory (LSTM)together to forecast air quality at high-resolution. Our model can utilize the spatial correlation characteristic of our air pollutant datasetsto achieve higher forecasting accuracy than existing deep learning models of air pollution forecast.
... A number of regional, global, and box models have been developed over the last 20 years to study atmospheric Hg cycling and deposition Bash, 2010;Bullock and Brehme, 2002;Hedgecock et al., 2003;Horowitz et al., 2017;Landis and Keeler, 2002;Lee et al., 2001;Pai et al., 1997;Sandu and Sander, 2006;Seigneur et al., 2001;Selin and Jacob, 2008;Strode et al., 2007;Ye et al., 2016). These modeling studies have greatly advanced our understanding of the behavior of Hg in the atmosphere. ...
... On the one hand, in virtue of the emissions from local anthropogenic sources such as coal-fired power plant, most Hg dry deposition rate came from larger particulates owing to the fact that the deposition velocity of coarse particulate was ordinarily higher than that of fine particulates (Sakata and Marumoto, 2004;Shimamura et al., 2006;Fang et al., 2012). For example, previous studies have suggested that the measured dry Hg P deposition velocities fluctuated between 0.31 and 0.94 cm s À1 with a mean of 0.59 cm s À1 in the Tokyo metropolitan area (Sakata and Marumoto, 2004), which were much higher than the values used for the atmospheric chemistry model calculations (e.g., Pai et al., 1997). On the other hand, Hg P was mainly associated with atmospheric particulates, and the dry deposition velocity of atmospheric particulate depends largely on meteorological conditions such as solar radiation, ambient temperature and wind speed (e.g., Wesely and Hicks, 2000;Zhang et al., 2009). ...
In an effort to understand the biogeochemical cycling and seasonal characteristics of atmospheric Hg, a total of 80 daily sampled total suspended particulates were collected at Lhasa, the largest city of Tibet, from April 2013 to August 2014 for particulate-bound Hg (HgP) analysis. Daily concentrations of atmospheric HgP ranged from 61.2 to 831 pg m−3 with an average of 224 pg m−3, which were unexpectedly comparable to those measured in most of the Chinese metropolises. Both the daily/monthly average HgP concentrations were slightly but not significantly higher during the non-monsoon season than during the monsoon season. Together with the fact that there was lack of significant relationship between HgP concentration and most meteorological parameters, no significant and distinct pattern for the seasonal characteristics of atmospheric HgP could be mainly attributed to the almost equal emission strength of two principal anthropogenic Hg sources (i.e., industrial emission sources during the non-monsoon season, and vehicular traffic and religious sources during the monsoon season). Moreover, the HgP dry deposition rate was estimated to be 35.3 μg m−2 yr−1 by using a theoretical model, which was significantly higher than those Hg wet fluxes. The elevated deposition rate implied that dry deposition may play an important role in the biogeochemical Hg cycling over the Tibetan Plateau.
... Of the three forms, oxidized mercury species are of great importance for the total deposition of mercury from the atmosphere according to an Eulerian model (Petersen et al. 1995). Although these species are typically present at less than 10% of the total atmospheric mercury, they appear to influence the deposition flux significantly (Petersen et al. 1996;Pai et al. 1997). ...
Mercury is outstanding among the global environmental pollutants of continuing concern. Especially in the last decade of the 20th century, environmental scientists, legislators, politicians and the public have become aware of mercury pollution in the global environment. It has often been suggested that anthropogenic emissions are leading to a general increase in mercury on local, regional, and global scales (Lindqvist et al. 1991; Expert Panel 1994).
... Atmospheric dry deposition is an important pathway for transferring PHg from atmosphere to the terrestrial and aquatic ecosystems (Fang et al., 2001). Although many uncertainties existed in estimating the dry deposition of PHg, the large dry deposition amounts of mercury (half or equal to wet deposition amounts) were found for many regions (Pai et al., 1997;Landis and Keeler, 2002). Moreover, previous studies have found elevated levels of mercury in pristine water bodies where there were few anthropogenic emission sources nearby (Swain et al., 1992;Rasmussen, 1994;Sorensen et al., 1994;Landis and Keeler, 2002), indicating that the atmospheric transport followed by deposition is a major pathway for the mercury contamination in remote areas (Miller et al., 2005). ...
Although present in a low concentration in the atmosphere, mercury in particulate matter (PHg) plays an important role in the biogeochemical process of mercury. In this study, the mercury concentrations in three size fractions of airborne particulate matters collected from 14 sites (12 urban sites, 1 rural site and 1 remote site) in the southeast coastal cities of China during different seasons in 2010-2011 were investigated. Most of PHg (46.8-71.9%) was concentrated in the finer particles, i.e. PM2.5 (particulate matter <= 2.5 mu m in aerodynamic diameter). The average mercury concentrations in PM2.5 were 141.2 +/- 128.1 (range of 7.6-956.5), 37.0 +/- 19.2 (5.6-89.4), and 24.0 +/- 14.6 (3.2-59.9) pg m(-3) at urban, rural, and remote sites during the whole sampling period, respectively. The PHg concentrations were almost at the same level in spring, autumn, and winter, approximately two times of that in summer. PHg concentrations in the atmosphere displayed a significant spatial variation with far higher values in urban areas than those at rural and remote sites. The dry deposition fluxes of total PHg estimated by a theoretical model were 38.3, 47.7, and 58.7 mu g m(-2) y(-1) at Ji'an (JA), Jimei (JM), and Longwen (LW), respectively. The backward air trajectory analysis revealed that the atmospheric PHg concentrations were mainly influenced by air masses from ocean sources that diluted PHg in summer and on contrary from continental sources in other seasons.
... A number of reviews have summarised published data concerning the long-range atmospheric transportation of mercury from industrial areas, and concluded that there is scientific evidence of a linkage between anthropogenic mercury emissions and elevated mercury concentrations in remote areas (Petersen et al. 1995;Jackson 1997a;Pai et al. 1997;Fitzgerald et al. 1998;Xu et al. 2000a;Xu et al. 2000b;Petersen et al. 2001;Wangberg et al. 2001). Measurements of mercury concentrations in ambient air support the conclusion that mercury deposited in remote areas may originate from anthropogenic sources far away. ...
... The mixing ratio of elemental mercury in this unit may be slightly lower than near the ground surface since descending vertical profile of the mixing ratio should exist. P. Pai et al. [1997] accept in their model that elemental mercury mass concentration at the boundary with the stratosphere is 70% of its near surface value. C. Banic et al. [1999] did not find any difference between concentrations near the ground and at the height of 7 km (within limits of measuring accuracy). ...
... The Hg associated with particulate matter which is directly emitted to the atmosphere is considered to be insoluble and is transported as a tracer species until it is either dry deposited or scavenged by cloud droplets and wet deposited. To calculate the dry deposition velocity we have followed the approach used by Pai et al. (1997) where the particle size distribution has been assumed to be log-normal with a geometric mass mean diameter of 0.3 µm and a geometric standard deviation of 1.5 µm. The deposition velocity is determined by dividing the distribution into a fixed number of size intervals, calculating the velocity for each interval and aggregating them in a weighted mean. ...
... Since 1996, in view of the upcoming UN-ECE heavy metals protocol and other environmental protection agreements such as the U.S/Canada Great Lakes Water Quality Agreement (GLWQA), an intensified scientific and political interest in comprehensive Eulerian model developments to derive estimates of ambient concentrations and dry and wet deposition fluxes of heavy metals over Europe [Bartnicki, 1998;Pirrone, 1998;Ryaboshapko et al., 1999;Lee et al., 2001] and North America [Pai et al., 1997, Bullock, 2000Seigneur et al., 2001] has been observed. These models are typical of the state-of-science models over the past several years and their main features show a couple of similarities. ...
... They suggested that chemical speciation and kinetics introduce the greatest uncertainties in atmospheric mercury modeling. Bullock et al. (2008) conducted a model intercomparison of the regional mercury models CMAQ (Bullock and Brehme, 2002), Regional Modeling System for Aerosols and Deposition (REMSAD) (ICF, 2005), and the Trace Element Analysis Model (TEAM) (Pai et al., 1997). They found signifi cant differences among the models, driven both by initial and boundary conditions and by model processes. ...
Reprint 2012-8 The MIT Joint Program on the Science and Policy of Global Change combines cutting-edge scientific research with independent policy analysis to provide a solid foundation for the public and private decisions needed to mitigate and adapt to unavoidable global environmental changes. Being data-driven, the Program uses extensive Earth system and economic data and models to produce quantitative analysis and predictions of the risks of climate change and the challenges of limiting human influence on the environment – essential knowledge for the international dialogue toward a global response to climate change. To this end, the Program brings together an interdisciplinary group from two established MIT research centers: the Center for Global Change Science (CGCS) and the Center for Energy and Environmental Policy Research (CEEPR). These two centers – along with collaborators from the Marine Biology Laboratory (MBL) at Woods Hole and short-and long-term visitors – provide the united vision needed to solve global challenges. At the heart of much of the Program's work lies MIT's Integrated Global System Model. Through this integrated model, the Program seeks to: discover new interactions among natural and human climate system components; objectively assess uncertainty in economic and climate projections; critically and quantitatively analyze environmental management and policy proposals; understand complex connections among the many forces that will shape our future; and improve methods to model, monitor and verify greenhouse gas emissions and climatic impacts.
... Numerous modeling studies have been conducted to understand the transport, chemistry and deposition of atmospheric mercury at regional (Baker and Bash, 2012;Bash et al., 2010;Bullock and Brehme, 2002;Bullock et al., 2009;Cohen et al., 2004;Gbor et al., 2007;Landis and Keeler, 2002;Lee et al., 2001;Lin and Tao, 2003;Lin et al., 2007;Lohman et al., 2006;Myers et al., 2013;Pai et al., 1997;Pongprueksa et al., 2008;Seigneur, 2003;Seigneur et al., 2001Seigneur et al., , 2003Seigneur et al., , 2004bSillman et al., 2007;Vijayaraghavan et al., 2007;Xu et al., 2000b;Zhang et al., 2012aZhang et al., , 2012b and global scales (Amos et al., 2012;Bergan and Rodhe, 2001;Bergan et al., 1999;Dastoor and Larocque, 2004;Holmes et al., 2006;Seigneur et al., 2006;Shia et al., 1999;Soerensen et al., 2010;Strode et al., 2007). Xu et al. (2000a) applied a three-dimensional chemical transport model (CTM) over an area of the northeastern United States, for a summer and a winter week to study the atmospheric transport and transformation of mercury. ...
The global-regional climate-air pollution modeling system (GRE-CAPS) was applied over the eastern United States to study the impact of climate change on the concentration and deposition of atmospheric mercury. Summer and winter periods (300days for each) were simulated, and the present-day model predictions (2000s) were compared to the future ones (2050s) assuming constant emissions. Climate change affects Hg(2+) concentrations in both periods. On average, atmospheric Hg(2+) levels are predicted to increase in the future by 3% in summer and 5% in winter respectively due to enhanced oxidation of Hg(0) under higher temperatures. The predicted concentration change of Hg(2+) was found to vary significantly in space due to regional-scale changes in precipitation, ranging from -30% to 30% during summer and -20% to 40% during winter. Particulate mercury, Hg(p) has a similar spatial response to climate change as Hg(2+), while Hg(0) levels are not predicted to change significantly. In both periods, the response of mercury deposition to climate change varies spatially with an average predicted increase of 6% during summer and 4% during winter. During summer, deposition increases are predicted mostly in the western parts of the domain while mercury deposition is predicted to decrease in the Northeast and also in many areas in the Midwest and Southeast. During winter mercury deposition is predicted to change from -30% to 50% mainly due to the changes in rainfall and the corresponding changes in wet deposition.
... [17] TEAM is a 3-D Eulerian model that simulates the transport, chemical and physical transformations, and removal of Hg species. The original formulation of TEAM was based on a polar stereographic projection [Pai et al., 1997]; this formulation was modified for this study and a Lambert conformal projection was used to allow full compatibility with the meteorological, emission and other inputs used by the other regional-scale models. [18] Transport processes include transport by the 3-D mean wind flow and dispersion by atmospheric turbulence. ...
1] An atmospheric mercury model intercomparison study has been conducted to compare three regional-scale atmospheric mercury models, CMAQ, REMSAD, and TEAM, in a tightly constrained testing environment with a focus on North America. Each of these models used the same horizontal modeling grid, pollutant emission information, modeled meteorology, and boundary conditions to the greatest extent practical. Three global-scale atmospheric mercury models were applied to define three separate initial condition and boundary condition (IC/BC) data sets for elemental mercury, reactive gaseous mercury, and particulate mercury air concentrations for use by the regional-scale models. The monthly average boundary concentrations of some mercury species simulated by the global models were found to vary by more than a factor of 10, especially at high altitudes. CMAQ, REMSAD, and TEAM were each applied three times, once for each IC/BC data set, to simulate atmospheric mercury transport and deposition during 2001. This paper describes the study design and shows qualitative model-to-model comparisons of simulation results on an annual basis. The air concentration patterns for mercury simulated by the regional-scale models showed significant differences even when the same IC/BC data set was used. Simulated wet deposition of mercury was strongly influenced by the shared precipitation data, but differences of over 50% were still apparent. Simulated dry deposition of mercury was found to vary between the regional-scale models by nearly a factor of 10 in some locations. Further analysis is underway to perform statistical comparisons of simulated and observed mercury wet deposition using weekly and annual sample integration periods.
... Information on the vertical distribution of mercury in the atmosphere is critically important for reliable estimates of the atmospheric mercury burden on local, regional and global scales. It is also an essential parameter in numerical models describing the biogeochemical cycling of mercury in the environment [Mason et al., 1994;Porcella, 1994;Mackay et al., 1995;Pai et al., 1997]. In addition, the role of clouds in the atmospheric cycling of mercury is poorly understood. ...
Measurements of gaseous elemental mercury (GEM) were made in three locations in Canada at altitudes from 0.1 to 7 km. In the summer in southeastern Canada, northwesterly winds bring air with a constant mixing ratio of GEM at altitudes up to 7 km, with a concentration near 1.5 nanograms per standard cubic meter of air (ng sm-3). In the winter in southern and central Ontario the mixing ratio is still approximately constant with altitude, but the concentration is 1.7 ng sm-3. In the spring in the Arctic the concentration of gaseous elemental mercury at altitudes above 1 km is near 1.7 ng sm-3 however, there is evidence of episodic depletion of elemental mercury near the surface with mixing of depleted air to altitudes of 1 km. Measurements of GEM in cloud interstitial air and of mercury in cloud water indicate that the influence of a single cycling of air through cloud has little effect on the concentration of GEM. The GEM in air masses transported over the relatively unpopulated terrain of northern Canada during the summer indicates a lower limit of 5000 ng m-2 for an atmospheric column from the surface to 5 km. This gives a global burden of at least 2500 t for that altitude range. These data demonstrate the existence of a vast pool of mercury aloft, provide evidence for a long atmospheric lifetime, and illustrate the potential for long-range atmospheric transport of this metal at altitudes up to at least 7 km.
... Dividing the assumed lognormal particle size distribution into a fixed number of size intervals, the deposition velocity is calculated for each interval and these are subsequently aggregated in a weighted mean. Parameter values for the size distribution, with a geometric mass mean diameter of 0.3 µm and a geometric standard deviation of 1.5 µm were taken from Pai et al. (1997). The calculation of aerodynamic resistance follows the same approach as for gaseous dry deposition, including the same distinction between types of landcover. ...
Mercury is a volatile metal, that is of concern because when deposited and transformed to methylmercury accumulates within the food-web. Due to the long lifetime of elemental mercury, which is the dominant fraction of mercury species in the atmosphere, mercury is prone to long-range transport and therefore distributed over the globe, transported and hence deposited even in regions far from anthropogenic emission sources. Mercury is released to the atmosphere from a variety of natural and anthropogenic sources, in elementary and oxidised forms, and as particulate mercury. It is then transported, but also transformed chemically in the gaseous phase, as well as in aqueous phase within cloud and rain droplets. Mercury (particularly its oxidised forms) is removed from the atmosphere though wet and dry deposition processes, a large fraction of deposited mercury is, after chemical or biological reduction, re-emitted to the atmosphere as elementary mercury. To investigate mercury chemistry and transport processes on the global scale, the new, global model ECHMERIT has been developed. ECHMERIT simulates meteorology, transport, deposition, photolysis and chemistry on-line. The general circulation model on which ECHMERIT is based is ECHAM5. Sophisticated chemical modules have been implemented, including gas phase chemistry based on the CBM-Z chemistry mechanism, as well as aqueous phase chemistry, both of which have been adapted to include Hg chemistry and Hg species gas-droplet mass transfer. ECHMERIT uses the fast-J photolysis routine. State-of-the-art procedures simulating wet and dry deposition and emissions were adapted and included in the model as well. An overview of the model structure, development, validation and sensitivity studies is presented.
... The correlation coefficient has been used to assess a number of mercury transport and transformation models [Ryaboshapko et al., 2002;Schmolke and Petersen, 2003;Xu et al., 2000;Lin and Tao, 2003;Bullock and Brehme, 2002], R Bias has been used in the EMEP intercomparison, [Ryaboshapko et al., 2002]. Comparison of standard deviation is used in the EMEP intercomparison, [Schmolke and Petersen, 2003;Bullock and Brehme, 2002)] although in the latter case to compare predicted and measured concentrations in precipitation; the index of agreement has been used by Lin and Tao [2003], and the graphical ''factor of two'' representations in the EMEP intercomparison report by Ryaboshapko et al. [2003], and also by Pai et al. [1997]. ...
The MECAWEx model (Pirrone et al., 2005) has been tested using measured total gaseous mercury data obtained during the four Mediterranean Atmospheric Mercury Cycle System (MAMCS) project measurement campaigns performed simultaneously at five coastal sites around the Mediterranean between 1998 and 1999. The model has also been tested using Hg(g)0, Reactive Gaseous Mercury (RGM) and Total Particulate Mercury (TPM) data from two oceanographic cruise campaigns. The model has been run for the whole 12 month period of the campaigns and thus has allowed annual deposition and emission fluxes to and from the Mediterranean Sea to be estimated. The results show that the combined wet and dry Hg deposition to the sea surface during the model run was 20.4 tons, while the emissions were 90.4 tons making the Mediterranean Sea a net emitter of Hg. The results allow the relative importance of wet and dry deposition pathways to be assessed over the modeling domain. The Mediterranean region as a whole is an area where the dry deposition flux of Hg almost always outweighs the wet deposition flux.
... Several models describing the fate and transport of gaseous mercury from a source through the atmospheric compartment to a receptor, at various scales have been developed (Pai et al. 1997;Shia 1999;Bullock 2000;Bergan and Rhode 2001;Sholtz and Van Heyst 2001). Modeling is limited by our knowledge on certain aspects of the biogeochemical cycle of mercury, such as the contribution from natural sources to the global atmospheric mercury budget (Bergan and Rhode 2001). ...
Since natural and anthropogenic sources can contribute to elevated levels of metals at remote and background sites, identifying the source of a metal is an important step in environmental risk assessment. Various source apportionment procedures are available to identify metal sources, and have been used extensively to determine sources in urban settings and to a lesser extent at remote sites. However, measuring metals at remote or background sites presents unique challenges with respect to experimental design. The state of the science in monitoring techniques and source apportionment procedures is discussed in terms of limitations and applicability to remote sites, and recommendations are made on maximizing information recovery through source apportionment procedures by incorporating appropriate experimental design.
... [3] Several three-dimensional (3-D) Eulerian grid-based models have been applied to Hg deposition in North America [Pai et al., 1997;Xu et al., 2000;Bullock and Brehme, 2002;Lin and Tao, 2003;Seigneur et al., 2004;Lin et al., 2006;Gbor et al., 2007;Sillman et al., 2007;Vijayaraghavan et al., 2007;Bullock et al., 2008;Selin and Jacob, 2008]. However, these traditional Eulerian gridbased models have several limitations when applied to the simulation of the fate of Hg and other emissions from elevated point sources such as power plant stacks. ...
An existing plume-in-grid model for ozone and particulate matter, which provides an explicit treatment of stack plumes embedded within a three-dimensional grid-based Eulerian air quality model, is extended to include a comprehensive treatment of mercury (Hg) processes. The model is applied to the continental United States to investigate the subgrid-scale effects associated with Hg emissions from large elevated point sources on atmospheric Hg concentrations and deposition. The top thirty Hg-emitting power plants in the U.S. were selected for explicit plume-in-grid treatment. Two new processes are included in the Hg chemical mechanism: the gas-phase adsorption of reactive gaseous mercury (RGM) on atmospheric particulate matter and the reduction of RGM to elemental Hg by sulfur dioxide. The plume-in-grid treatment results in improved performance for Hg wet deposition over a purely Eulerian grid-based model, partial correction of overpredictions of wet deposition downwind of coal-fired power plants in the northeastern U.S., and decreases of approximately 10% in simulated dry and wet deposition over large parts of the eastern U.S., with larger decreases near the plants selected for plume-in-grid treatment. On average, 23% of ambient RGM is modeled to adsorb on atmospheric particulate matter.
... The majority of mercury in precipitation is in the ionic Hg 2+ form, however a small amount of MeHg may also be deposited via this route. Hg 2+ is removed very efficiently relative to other species by both dry and wet deposition due to its high solubility and high deposition velocity [36]. Although the amount of methyl mercury in precipitation has not been measured in the Passamaquoddy Bay region, this fraction is estimated as ~1% of total deposition based on results of a number of other studies [37, 38] . ...
... Since gaseous Hg deposition rates are difficult to directly measure (Lyman et al., 2007) and are highly variable over space and time (diurnally and seasonally ), long-term depositional studies often ''infer " them as the product of the species-specific air concentrations and an empirical deposition velocity (V d ). Hourly V d is often calculated using a resistance model, on-site meteorology, and site-specific land use parameters (Lindberg et al., 1992; Pai et al., 1997 Pai et al., , 1999 Lin et al., 2006). The primary objectives of this study were to obtain seasonal measurements of Hg air concentrations in the SFCR area and to estimate annual dry deposition rates in the area. ...
Gaseous elemental mercury (GEM) and reactive gaseous mercury (RGM) were measured over 2-week seasonal field
campaigns near Salmon Falls Creek Reservoir in south-central Idaho from the summer of 2005 through the fall of
2006 and over the entire summer of 2006 using automated Tekran Hg analyzers. GEM, RGM, and particulate Hg
(HgP) were also measured at a secondary site 90 km to the west in southwestern Idaho during the summer of 2006.
The study was performed to characterize Hg air concentrations in the southern Idaho area for the first time, estimate
Hg dry deposition rates, and investigate the source of observed elevated concentrations. High seasonal variability was
observed with the highest GEM (1.91 ± 0.9 ng m�3) and RGM (8.1 ± 5.6 pg m�3) concentrations occurring in the summer
and lower values in the winter (1.32 ± 0.3 ng m�3, 3.2 ± 2.9 pg m�3 for GEM, RGM, respectively). The summer-average
HgP concentrations were generally below detection limit (0.6 ± 1 pg m�3). Seasonally averaged deposition velocities calculated
using a resistance model were 0.034 ± 0.032, 0.043 ± 0.040, 0.00084 ± 0.0017 and 0.00036 ± 0.0011 cm s�1 for
GEM (spring, summer, fall and winter, respectively) and 0.50 ± 0.39, 0.40 ± 0.31, 0.51 ± 0.43 and 0.76 ± 0.57 cm s�1
for RGM. The total annual RGM + GEM dry deposition estimate was calculated to be 11.9 ± 3.3 lg m�2, or about 2/
3 of the total (wet + dry) deposition estimate for the area. Periodic elevated short-term GEM (2.2–12 ng m�3) and
RGM (50–150 pg m�3) events were observed primarily during the warm seasons. Back-trajectory modeling and PSCF
analysis indicate predominant source directions to the SE (western Utah, northeastern Nevada) and SW (north-central
Nevada) with fewer inputs from the NW (southeastern Oregon and southwestern Idaho).
Published by Elsevier Ltd.
... [3] Several three-dimensional (3-D) Eulerian grid-based models have been applied to Hg deposition in North America [Pai et al., 1997;Xu et al., 2000;Bullock and Brehme, 2002;Lin and Tao, 2003;Seigneur et al., 2004;Lin et al., 2006;Gbor et al., 2007;Sillman et al., 2007;Vijayaraghavan et al., 2007;Bullock et al., 2008;Selin and Jacob, 2008]. However, these traditional Eulerian gridbased models have several limitations when applied to the simulation of the fate of Hg and other emissions from elevated point sources such as power plant stacks. ...
An existing plume-in-grid model for ozone and particulate matter, which provides an explicit treatment of stack plumes embedded within a three-dimensional grid-based Eulerian air quality model, is extended to include a comprehensive treatment of mercury (Hg) processes. The model is applied to the continental United States to investigate the subgrid-scale effects associated with Hg emissions from large elevated point sources on atmospheric Hg concentrations and deposition. The top thirty Hg-emitting power plants in the U.S. were selected for explicit plume-in-grid treatment. Two new processes are included in the Hg chemical mechanism: the gas-phase adsorption of reactive gaseous mercury (RGM) on atmospheric particulate matter and the reduction of RGM to elemental Hg by sulfur dioxide. The plume-in-grid treatment results in improved performance for Hg wet deposition over a purely Eulerian grid-based model, partial correction of overpredictions of wet deposition downwind of coal-fired power plants in the northeastern U.S., and decreases of approximately 10% in simulated dry and wet deposition over large parts of the eastern U.S., with larger decreases near the plants selected for plume-in-grid treatment. On average, 23% of ambient RGM is modeled to adsorb on atmospheric particulate matter.
... [7] Recent global Hg models have incorporated the dry deposition of RGHg derived from point source emissions, even though the database of reliable measurements is small, and have shown that RGHg deposition can have an impact on a local/regional scale [Shia et al., 1999;Bullock et al., 1997;Bullock, 2000;Pai et al., 1997Pai et al., , 1999Xu et al., 2000]. However, these models, which also incorporate oxidation-reduction chemistry of Hg during cloud formation and wet deposition, have not incorporated the deposition of RGHg formed in remote regions by all the potential gas phase or heterogeneous reactions in the atmosphere; in particular, the oxidation of Hg o by halogen radicals. ...
Air-sea exchange of mercury (Hg) is a critical part of the global Hg cycle as it determines, to a large degree, the response time of the biosphere to changes in mercury inputs. Recent measurements have demonstrated that the cycling of Hg between the ocean and atmosphere is complex, principally because of the enhanced oxidation of elemental Hg (Hgo), and the formation of reactive gaseous Hg (RGHg) in the marine boundary layer. We estimate that the dry deposition of RGHg to the ocean, which has not been previously considered in global budgets, is 35% of the total Hg input to the ocean. A further reevaluation of the global Hg cycle suggests that there is a net transfer of Hg from the terrestrial environment to the ocean and that the deep ocean Hg concentration is increasing by a few percent per year. Similarly, anthropogenic inputs on land have increased Hg on the Earth's surface layer with accumulation in the terrestrial environment accounting for nearly 80% of the net input from man's activities. Dry deposition of RGHg is important for the terrestrial realm but because of its relatively short residence time in the atmosphere, it is the oxidation of Hgo over the ocean, rather than RGHg transport offshore, which is primarily contributing to oceanic RGHg deposition.
The control of mercury emission from flue gas has long been a serious task for the global environment and human health. Utilization of selective catalytic reduction (SCR) catalysts to oxidize Hg⁰ to form Hg²⁺ and subsequent capture the Hg²⁺ through a wet flue gas desulfurization (WFGD) scrubber is an efficient and economical technology for Hg⁰ removal in coal-fired power plants. Extensive studies have been conducted with regard to Hg⁰ oxidation over SCR catalysts. However, recent studies found that the reduction of Hg²⁺, an inverse process to Hg⁰ oxidation, also occurred even predominated under some SCR conditions. This new observation overturns the general knowledge that SCR catalysts always enhance Hg⁰ oxidation. To avoid the neglect of Hg²⁺ reduction and overcome the shortages of existing studies, a critical review of Hg²⁺ reduction over SCR catalysts was undertaken. The Hg²⁺ reduction behaviors under various SCR conditions were summarized and the effects of typical flue gas components like hydrogen chloride (HCl), sulfur dioxide (SO2), water vapor (H2O), volatile organic compounds (VOCs), and carbon monoxide (CO) on Hg²⁺ reduction were also presented. The involved reaction mechanisms for Hg²⁺ reduction were discussed in details. Moreover, feasible measures to suppress the reduction of Hg²⁺ in the SCR system were proposed. We expect to clearly explore the mechanism of the Hg⁰ redox process on SCR catalysts in this review to avoid the neglect of Hg²⁺ reduction, hence providing guidance for the design of SCR catalysts to achieve an efficient Hg⁰ oxidation.
To simulate global mercury (Hg) dynamics in chemical transport models (CTMs), surface-atmosphere exchange of gaseous elemental mercury, Hg0, is often parameterized based on resistance-based dry deposition schemes coupled with a...
Trajectory cluster analysis and the potential source contribution function (PSCF) model have been used to investigate the source-receptor relationship for the total gaseous mercury (TGM) measured in the Canadian High Arctic (Alert, 82.5 degreesN, 62.3 degreesW) during 1995. Cluster analysis of 10-day back-trajectories in 1995 shows that the synoptic flows arriving at Alert are dominated by the air masses from the north. Long-range transport only occurs in the cold seasons while summertime flows tend to circulate in the Arctic Ocean. The potential source regions identified by the PSCF modeling include Eurasia and populated areas in the North America and Europe. Based on the modeling results, it is suggested that the elevated TGM concentrations found in the Arctic summer should be of geological origins, mainly from the evasion of volatile Hg-0 from earth's surfaces. In the autumn and winter, mercury is transported to the receptor site from remote anthropogenic sources. The preferred sources of TGM in the spring cannot be clearly determined due to the Arctic springtime mercury depletion, which significantly reduces the number of trajectories contributing to PSCF values. Using TGM data of higher temporal resolution improves the sensitivity of the PSCF modeling results.
Despite progress in the last decade in the research of Hg emission from soils, considerable knowledge gaps still exist and point to the need for further extensive and elaborate research in this field. In this chapter, we discuss these uncertainties and identify some future priorities for the research of soil Hg emission. Our intension is to promote a more extensive and critical assessment of our current knowledge and understanding on soil Hg emissions and their effect on global Hg cycling.
In order to better define the cycling of mercury in the global troposphere, we have studied over the past four years the homogeneous gas-phase reaction of elemental mercury (Hg0) with hydrogen peroxide (H2O2), 03, methyl iodide (CH3I), and dimethyl sulfide ((CH3)2S or DMS) in FEP Teflon® reactors. For the first time, we report laboratory measurements of the reaction rate constant of Hg0 with H202. Results which were at or below our detection limit suggest this reaction must have a rate constant of <8.5 x 10−19 cm3 molecule−1 s−1. With 8.5 x 10−19 cm3 molecule−1 s−1 as an upper limit rate constant, mean H202 concentrations of 1.0 ppb would yield a global average Hg0 residence time of 1.5 years, similar to that calculated by reaction with 30 ppb 03. Methyl iodide or (CH3)2S are not geochemically important in the cycling of gaseous Hg0. New research should focus on both the homogeneous and heterogeneous reactions of Hg0 with Cl2 and other reactive CI species, OH, HO2 and organic peroxyradicals (RO2).
This paper presents a comprehensive atmospheric global and regional mercury model and its capability in describing the atmospheric cycling of mercury. This is an on-line model (integrated within the Canadian operational environmental forecasting and data assimilation system) which can be used to understand the role of meteorology in mercury cycling (atmospheric pathways), the inter-annual variability of mercury and can be evaluated against observations on global scales. This is due to the fact that the model uses a combination of actual observed and predicted meteorological state of the atmosphere at high resolution to integrate the model as opposed to the climatological approach used in existing global mercury models. The model was integrated and evaluated on global scale using only anthropogenic emissions. North to south gradients in mercury concentrations, seasonal variability, dry and wet deposition and vertical structure are well simulated by the model. The model was used to explain the observed seasonal variations in atmospheric mercury circulation. The results from this study include a global animation of surface air concentrations of total gaseous mercury for 1997.
A source-specific, spatially resolved mercury emission inventory is a key input to an air-quality model that is used to understand relationships between mercury emissions and observed deposition. Previously we simulated the transport and deposition of anthropogenic mercury emissions in the contiguous United States. Due to the long residence time of elemental mercury, i.e., 1 year, it is possible that mercury deposition observed at receptors in the US could be due to long-range transport of emissions across political boundaries. We have recently added mercury emission estimates of anthropogenic sources in Canada and Mexico, to our US inventory. This combined inventory will be used with a regional model to understand source–receptor relationships of atmospheric mercury emissions in North America. Our estimate of 272 Mg of mercury emissions from various anthropogenic sources in North America is comparable to estimates in global inventories (ranging from 240 to 333 Mg). In this paper we discuss the differences in the three regional inventories, i.e., US, Canada, and Mexico, for the year 1990. The dominant source categories of mercury emissions in 1990 in the three regions are different. While combustion of municipal waste and coal accounts for 56% of the 176 Mg mercury emissions in the US in 1990, smelting of nonferrous metals represents the largest source of mercury emissions in Canada (=24 Mg) and Mexico (=31 Mg) in 1990. The main source of uncertainty in the emission estimates is due to the emission factors used in estimation. The emission factors are derived from measurements at a limited number of sources and could potentially not be representative of the operating conditions at other sources for which they are used. In addition, the inventories could still be missing potentially important source categories due to lack of data to develop reliable emission factors. These sources of uncertainties are common features of all three inventories and clearly point to additional research needs.
Currently, there is not a coordinated observational network for mercury (Hg) that could be used by the modelling community
or for establishing recommendations for protecting human and environmental health on a global scale. Current national networks
are inadequate as they lack (1) observations of all forms of Hg in the ambient air and in both wet and dry deposition; (2)
long-term measurements of Hg and other air pollutants; (3) comprehensive monitoring sites in the free-troposphere; and (4)
measurement sites that permit a careful investigation of inter-hemispheric transport and trends in background concentrations.
Programs such as the World Meteorological Organization's Global Atmosphere Watch have made substantial efforts to establish
data centers and quality control programs to enhance integration of air quality measurements from different national and regional
networks, and to establish observational sites in under-sampled, remote regions around the world. Similarly, the International
Global Atmospheric Chemistry project (of the International Geosphere-Biosphere Programme) has strongly endorsed the need for
international exchange of calibration standards and has helped coordinate multinational field campaigns to address a variety
of important issues related to global air quality. Following the lead of these programs and incorporation of a well-defined
Hg monitoring component into the existing network sites would be the most expeditious and efficient approach. Close coordination
of the global modelling community with the global measurement community would lead to major advances in the global models
and advance our understanding of the Hg science while decreasing the uncertainties in global assessments for Hg.
This work summarizes field studies that have been carried out to investigate the chemistry and environmental behavior of atmospheric mercury on different spatial and temporal scales in North-western and Central Europe. The spatial scales cover local and regional dimensions. Temporal scales include short-term variations of atmospheric mercury concentrations within less than one hour, variations that typically occur within time steps of a few hours to several days and long-term observations that cover almost three decades. The knowledge of the worldwide trend of atmospheric mercury concentrations during the last few decades is valuable for at least two reasons. The trend may reveal the impact of the control measures (OECD, 1994; US EPA, 1997) on the global cycle of atmospheric mercury. The response of mercury concentrations to the control measures may also provide information about the poorly defined ratio of anthropogenic to natural emissions (Schroeder and Munthe, 1998; Ebinghaus et al, 1999a). Slemr et al. (2003) have attempted to reconstruct the worldwide trend of total gaseous mercury (TGM) concentrations from long term measurements of known documented quality (Ebinghaus et al., 1999b) on 6 sites in the northern hemisphere (NH), 2 sites in the southern hemisphere (SH), and 8 ship cruises over the Atlantic Ocean made intermittently since 1977.(figure presented) The data presented in Figure 1 shows a generally good agreement between ship TGM measurements over the northern Atlantic Ocean and land-based measurements at Mace Head (Ireland), Lista, and Ny Ålesund (both Norway). The measurements at Mace Head also agree excellently with those made at Alert (Canada). TGM median values at the summit of the Wank mountain in southern Germany tend to be higher, most likely due to emissions in western and central Europe. Measurements at Rorvik in Sweden tend to provide the lowest values in the NH but are still in reasonable agreement with measurements at Alert and Lista (see also discussion in Munthe et al., 2003). All data, when taken together, suggest that the TGM concentrations in the NH had been increasing since the first measurements in 1977 to a maximum in the 1980s (most likely in the 2nd half (Slemr et al., 2003), then decreased to a minimum in 1996 and have remained constant since that time at a level of about 1.7 ng m-3. Slemr et al. (2003) claim that the observed temporal profile is primarily the result of the temporal change of mercury emissions. The temporal trend is qualitatively consistent with changes in global anthropogenic emissions (e.g. Pacyna and Pacyna, 2002; Pirrone et al, 1996) emphasising that the analysis of emission changes may help to explain observed long-term trends. However, these estimates do not reflect the measured decrease from 1990 to 1996 (Slemr et al., 2003).
Previously, we have simulated the atmospheric transport and fate of mercury emissions in North America and derived estimates of ambient concentrations and dry and wet deposition of mercury. In this study we quantify sensitivity of the derived estimates to model input parameters that we believe have the largest potential to influence model estimates. We vary five input parameters: emission speciation, Hg(II) dry deposition velocity, precipitation amount, concentration of redox species, and Hg(II) boundary conditions, within their plausible range of values. Our results show that emission speciation has the largest influence and Hg(II) boundary conditions have the smallest influence on the derived estimates. The sensitivity of simulated wet deposition to emission speciation and redox species concentration is non-linear and varies by region. In regions with low wet deposition (5-15 mugm-2yr-1), emission speciation and chemistry show comparable influence, whereas in regions with high wet deposition (15-30 mugm-2yr-1), emission speciation shows greater influence than chemistry. The interregional differences in sensitivity suggest that different pathways control total wet deposition for different regions. While in our previous study we evaluated the modeling system against observations, the sensitivity studies described in this paper enabled us to obtain new insights on atmospheric mercury by focusing on the dynamics of the system, i.e., response of the system to variation in its inputs. This analysis is essential before model-simulated results are used to investigate source-receptor relationships. Our findings also indicate that there is a critical need to get additional data on mercury speciation of major emission sources.
Most studies on the atmospheric behaviour of mercury in North America have excluded a detailed treatment of natural mercury emissions. The objective of this work is to report a detailed simulation of the atmospheric mercury in a domain that covers a significant part of North America and includes not only anthropogenic mercury emissions but also those from natural sources including vegetation, soil and water.The simulations were done using a natural mercury emission model coupled with the US EPA's SMOKE/CMAQ modelling system. The domain contained 132×90 grid cells at a resolution of 36km, covering the continental United States, and major parts of Canada and Mexico. The simulation was carried out for 2002, using boundary conditions from a global mercury model. Estimated total natural mercury emission in the domain was 230 tonnes (1 tonne=1000kg) and the ratio of natural to anthropogenic emissions varied from 0.7 in January to 3.2 in July. Average total gaseous mercury (TGM) concentration ranged between 1 and 4ngm−3. Good agreement was found between the modelled results and measurements at three Ontario sites for ambient mercury concentrations, and at 72 mercury deposition network sites in the domain for wet deposition. The correlation coefficient between the simulated and the measured values of the daily average TGM at three monitoring sites varied between 0.48 and 0.64. When natural emissions were omitted, the correlation coefficients dropped to between 0.15 and 0.40. About 335 tonnes of mercury were deposited in the domain during the simulation period but overall, it acted as a net source of mercury and contributed about 21 tonnes to the global pool. The net deposition of mercury to the Great Lakes was estimated to be about 2.4 tonnes. The estimated deposition values were similar to those reported by other researchers.
Previously, we have simulated the atmospheric transport and fate of mercury emissions in Europe and derived estimates of ambient concentrations and dry and wet deposition of mercury species using a mercury version of the Acid Deposition and Oxidants Model (ADOM). In this study, we focus on comparisons of model results against observations from European measuring campaigns performed between 1995 and 1999 in the framework of the Germany–Canada Science and Technology Co-operation Agreement and the Mercury Species over Europe (MOE) project funded by the European Commission. Simulations were conducted using 1997/1998 meteorology and 1990 emission inventories. Model simulations show a good performance in explaining the peak mercury concentrations on a 800km south to north transect, which were represented by simultaneous measurements at four sampling sites. Regional concentration gradients and differences in the concentration variability are well reproduced by the model even on a time base of 1h.
We present a numerical approach for solving the free boundary problem for the Black-Scholes equation for pricing American style of floating strike Asian options. A fixed domain transformation of the free boundary problem into a parabolic equation defined on a fixed spatial domain is performed. As a result a nonlinear time-dependent term is involved in the resulting equation. Two new numerical algorithms are proposed. In the first algorithm a predictor-corrector scheme is used. The second one is based on the Newton method. Computational experiments, confirming the accuracy of the algorithms, are presented and discussed.
Atmospheric concentrations of elemental (Hg(0)), reactive gaseous (RGM), and particulate (PHg) mercury were measured at two remote sites in the midwestern United States. Concurrent measurements of Hg(0), PHg, and RGM obtained at Devil's Lake and Mt. Horeb, located approximately 65 kin apart, showed that Hg(0) and PHg concentrations were affected by regional, as well as local sources, while RGM was mainly impacted by local sources. Plumes reaching the Devil's Lake site from a nearby coal-fired power plant significantly impacted SO(2) and RGM concentrations at Devil's Lake, but had little impact on Hg(0). Our findings suggest that traditional modeling approaches to assess sources of mercury deposited that utilize source emissions and large-scale grids may not be sufficient to predict mercury deposition at sensitive locations due to the importance of small-scale sources and processes. We suggest the use of a receptor-based monitoring to better understand mercury source-receptor relationships.
A numerical simulation of the atmospheric fate and transport of mercury (Hg) was conducted using a multiscale approach. Two different spatial scales were used to simulate (1) the global cycling of atmospheric Hg and (2) the atmospheric deposition of Hg in potentially sensitive areas. The global simulation was conducted using an updated version of our global Hg chemical transport model (CTM). The imbedded continental simulation was conducted using an updated version of the regional/continental CTM, TEAM. Simulations were conducted using 1998 meteorology and 1998/1999 emission inventories. Model simulation results show improved performance compared to earlier simulations. For example, the global simulation shows background concentrations of Hg species, interhemispheric gradients, and vertical gradients that are consistent with available measurements. The comparison of simulated Hg wet deposition fluxes with data from the Mercury Deposition Network in the United States shows a coefficient of determination (r 2) of 0.75, little bias (−3%), and an average gross error of 21%. The major remaining sources of uncertainties, which include speciation of Hg emissions, Hg atmospheric chemistry, and dry and wet deposition processes for Hg species, are discussed.
A multiscale modeling system that consists of a global cycling model and a continental-scale model, TEAM, is applied to simulate the fate and transport of mercury over North America. The performance of the modeling system is shown to be satisfactory. TEAM is used to simulate three coal-fired power plant emission control scenarios that correspond to 47%, 30% and 16% reductions in mercury emissions from the 1999 base case. Changes in total mercury deposition are less than 10% over most of the United States. The latter two scenarios that include subcategorization of power plants by coal rank and stack temperature show little effect on mercury deposition compared to the first scenario.
Two modified passive samplers were evaluated at multiple field locations. The sampling rate (SR) of the modified polyurethane foam (PUF)-disk passive sampler for total gaseous mercury (TGM) using gold-coated quartz fiber filters (GcQFF) and gaseous oxidized mercury (GOM) using ion-exchange membranes (IEM) were 6.4 AE 1.4 and 15.3 AE 0.3 m 3 day À1 , respectively. The relative percent difference between TGM and GOM concentrations measured by a Tekran system and the passive samplers averaged 19 AE 14 and 13 AE 12% and ranged between 4–44 and 1.5–41%, respectively. The GcQFF and IEM substrates were also evaluated as collection media for surrogate surface dry deposition measurements. Mercury (Hg) concentration and dry deposition gradients were observed using these samplers at an urban/industrial site and compared to a rural/remote site. The Hg dry deposition rates measured by the surrogate surfaces were always higher than those calculated by a widely used inferential modeling method (1.3–50 fold). The Hg dry deposition measured at urban and suburban sites were comparable to those calculated from model. However, they were very different at a rural site, probably due to the low concentrations. Both methods are relatively low cost and will aid in understanding spatial distributions of Hg ambient air concentrations and dry deposition.
We have modified recently published dry deposition models to estimate deposition velocities (Vd) for Hg in both fine aerosol and vapor form to forest canopy surfaces. Aerosol and total vapor phase Hg concentrations in air previously measured at Walker Branch Watershed in Tennessee have been used with model results to estimate dry deposition to a deciduous forest. The concentration data confirm that airborne Hg is dominated by vapor forms at this site and exhibits concentrations moderately above continental background levels. The modeled Vd values reflect published data which suggest that dry deposition of Hg vapor is strongly controlled by surface transport processes, notably stomatal and mesophyll resistances, the latter dominating. Weekly mean Vd values ranged from 0.006 (winter) to 0.12 (summer) cm s-1. We have also measured concentration gradients of Hg vapor in air above this forest to estimate air-surface exchange during short-term experiments. While the model results indicate that the canopy is a sink for Hg vapor, the concentration profiles suggest that the forest soils are a source during some periods, the combined effect of which is net Hg fluxes in the upward direction. Application of a detailed canopy turbulence model yielded soil emission rates of the order of 50 ng Hg m-2 h-1, ~10% of which is deposited in the canopy. Our modeled dry deposition estimates plus limited measurements of wet deposition in this area suggest that dry and wet deposition may be comparable in magnitude.
A three dimensional diagnostic wind field model is shown to be capable
of generating potential flow solutions associated with simple terrain
features. This is achieved by modifying an initially uniform background
wind to make the flow divergence free. Atmospheric stability effects can
be incorporated by considering the relative degree of adjustment that is
allowed between the horizontal and vertical components of the wind.A
framework for developing a Froude-number-dependent expression for this
ratio is proposed and evaluated by comparing modeled streamline
deflections of flow past an ideal hill with results from wind tunnel and
tow tank experiments.
Historical studies for crop and weed species documented elemental Hg vapor (Hg) deposition to foliage, but they used Hg concentrations that were orders of magnitude higher than levels now known to occur under background conditions, possibly creating artificially high gradients between the atmosphere and landscape surfaces. Measurements of Hg exchange with white oak (Quercus alba L.), red maple (Acer rubrum L.), Norway spruce (Picea abies L.), and yellow-poplar (Liriodendron tulipifera L.) foliage were conducted in an open gas exchange system that allows for simultaneous measurements of CO2, H2O and Hg exchange under controlled environmental conditions. When Hg concentrations were held at 0.5 to 1.5 ng m–3, red maple (Acer rubrum L.), Norway spruce (Picea abies L.), yellow-poplar (Liriodendron tulipifera L.), and white oak (Quercus alba L.) foliage exhibited mean Hg emissions of 5.5, 1.7, 2.7, and 5.3 ng m–2 h–1, respectively. At Hg concentrations between 9 and 20 ng m–3 little net exchange of Hg was observed. However at concentrations between 50 and 70 ng m–3 the Hg was deposited to foliage at rates between 22 and 38 ng m–2 h–1. These data suggest that dry foliar surfaces in terrestrial forest landscapes may be a dynamic exchange surface that can function as a source or sink dependent on the magnitude of current Hg concentrations. These data provide evidence of species-specific compensation concentrations (or compensation points) for Hg deposition to seedling foliage in the 10–25 ng m–3 range.
The primary goal of the Florida Atmospheric Mercury Study (FAMS) is to quantify the seasonal and geographical variability in the atmospheric deposition of Hg and other trace elements in central and south Florida. Precipitation, aerosol, and gaseous Hg samples have been collected at seven sites in Florida for periods ranging from 3 to 24 months. The summertime wet season in south Florida accounts for 80 to 90% of the annual rainfall Hg deposition. Depositional rates in south Florida are 30 to 50% higher than those from central Florida. Particle phase measurements range from 2 to 18 pg/m3Hg at all sites. Measurements of monomethylmercury in precipitation range from
The importance of participate mercury (Hg(p)) in the transport, chemistry and deposition of this toxic metal has long been underestimated and largely ignored. While it was once believed to constitute a small percentage of total atmospheric mercury, Hg(p) may contribute a significant portion of the deposition of this metal to adjacent natural waters. Recent measurements of Hg(p) in several urban/industrial areas have documented that Hg can be associated with large particles (>2.5 m) and in concentrations similar to those of the vapor phase Hg (ng/m3). As part of ongoing effort to diagnose the sources, transport and deposition of Hg to the Great Lakes and other Great Waters, the University of Michigan Air Quality Laboratory (UMAQL) has investigated the physical and chemical properties of particulate-phase Hg in both urban and rural locations. It appears that particulate Hg may be the one of the most difficult of the Hg measurements to perform, and perhaps the one of the most important for deposition and source apportionment studies. Particulate Hg concentrations measured in rural areas of the Great Lakes Region and Vermont ranged from 1 to 86 pg/m3 whereas Hg(p) levels in urban/industrialized areas were in the range 15 pg/m3 to 1.2 ng/m3.
Deposition velocity fields were generated for SO2, sulfate and HNO3 over eastern United States and southeastern Canada by combining detailed landuse data with meteorological information predicted using a mesoscale meteorology model. When there is significant variation in land type within an averaging area, it was found that subgrid scale meteorological variations can significantly influence area-averaged deposition velocities. The assumption that uu is constant over the averaging area can realistically address the subgrid variations in wind speed and friction velocity. For a 3-day springtime simulation, domain-averaged mid-day SO2, sulfate and HNO3 deposition velocities at a height of approximately 40 m were found to be 0.8 cm s−1, 0.2 cm s−1, and 2.5 cm s−1, respectively. At night, the deposition velocities were approximately 50%, 45% and 70% of the corresponding daytime values for SO2, sulfate and HNO3. Using a simple parameterization to account for rainfall-wetted surfaces increased domain-averaged SO2 deposition velocities by up to a factor of two, indicating that precipitation can significantly enhance dry deposition of SO2.
Santiago frequently experiences episodes of high air pollutant concentrations, particularly during the winter months. These episodes are a consequence of the unique geographic setting of the Santiago region and emissions of large quantities of pollutants by various surface sources such as diesel buses, automobiles, and wood burning, and point sources such as power plants and smelters. The modeling system consists of a set of air quality models to be used for air quality evaluation and planning in the region. The principal model in the system is a 3-dimensional terrain-following Eulerian model which incorporates a state-of-the-art gas-phase chemical mechanism to simulate the photochemical production of oxidants. This paper describes the special features of the modeling region, the diagnostic wind field preprocessor and the Eulerian model. There is a short general discussion at the end of the article. -from Authors
This paper examines the performance of two advection schemes in simulating a multiday ozone episode in the San Joaquin Valley of California. The advection schemes, viz. the flux conserving Smolarkiewicz scheme and a semi-Lagrangian scheme, were tested within the framework of a three-dimensional Eulerian comprehensive photochemical model. The modeling framework allowed us to test the performance of the advection schemes for the following two realistic test cases: (a) transport of inert species under the realistic flow conditions occurring during the ozone episode, and (b) transport of ozone precursors and formation of ozone during the four day episode. Our results indicate that the semi-Lagrangian scheme is not sensitive to deviations from mass consistency of the wind field, which is especially important in photochemical models that are driven by diagnostic meteorological models, such as the model used in the present study. Furthermore, we show that the semi-Lagrangian scheme preserves concentration peaks better than the more diffusive flux-conserving Smolarkiewicz scheme, used currently in a few operational photochemical models.
A non-linear three-dimensional grid model was used to derive source-receptor relationships, referred to as transfer coefficients, for visibility reducing species (such as sulfate) for 78 sources and 16 Class I receptors in the western United States for the calendar year 1992. The transfer coefficients will be used to assess the impact of changes in emissions on visibility at sensitive receptors, such as the Grand Canyon National Park. Uncertainties associated with model inputs and model formulation and assumptions lead to uncertainties in the derived transfer coefficients. This paper examines the uncertainties in the source-receptor relationships that are associated with grid resolution as well as the effect of assuming that levels of SO2 oxidants, such as H2O2, do not change when calculating transfer coefficients.
Most of the information required to estimate the concentration of a pollutant released in the planetary boundary layer is contained in three variables namely the surface friction velocity u*, the convective velocity scale w* and the mixed layer height zi. Although these variables are more directly related to the dispersive ability of the PBL than the various stability classification schemes their use has been largely ignored by the air pollution modeling community. This situation is a result of the relative lack of acceptable methods to relate these variables to routinely available meteorological measurements such as wind speed and solar radiation. In this note we present some techniques to do just this. We will also briefly describe the use of these variables in air pollution modeling.
Based on a simple principle, a method of obtaining an objective analysis is considered. Techniques of the calculus of variations are employed. Using this principle, two cases are studied. Case I is based on the assumption of quasi-geostrophic and thermal wind conditions. Case II is based on conditions defined by non-divergence and the “balance equation” which correspond to an equivalent barotropic flow. The method is demonstrated by three simple examples.
A chemical scheme based upon current knowledge of physicochemical forms and transformation reactions of atmospheric mercury has been implemented into a regional pollutant dispersion model for Europe. Existing databases for anthropogenic mercury emissions in Europe have been updated for 1987 and 1988 using new information on source data from eastern European countries including the former German Democratic Republic. Concentrations of total gaseous and particle associated mercury in air and mercury in precipitation calculated by the model are compared with observed values at Roervik in southwestern Sweden, Aspvreten, south of Stockholm and other locations of the Nordic network, on a daily basis. The results show that the model is capable of simulating long-range transport of mercury from Central Europe to Scandinavia including discrete events with peak concentrations in air and precipitation in the range of 10 ng m−3 and 100 ng −1, respectively. Coinciding observed and calculated peak concentrations indicate that exceptionally high mercury emissions, most probably from chlor-alkali industry and lignite coal combustion in East Germany and Czechoslovakia, must have occurred in 1987 and 1988.
We used the modified Bowen ratio method to estimate the fluxes of vapor-phase elemental Hg (Hg0) over background forest soils during the summer and fall of 1993. Fluxes were derived from the concentration gradients of total gaseous Hg between sampling heights of 25 and 165 cm and the concurrently determined turbulent diffusion coefficients of reference trace gases (i.e. H2O or CO2). The concentration and gradient data of Hg0 measured during the campaigns generally fell in relatively narrow ranges of 1.52–3.68 and −0.16 to 0.32 ng m−3 (over 140 cm), respectively: means ( ± 1 S.D.) for the corresponding; emission and deposition fluxes were found to be 7.5 ± 7.0 (n= 30) and −2.2 ± 2.4 ng m−2 h−1 (n=9), respectively. From the data collected during a series of sequential measurements, reproducible patterns of diurnal exchange emerged: (1) small bidirectional fluxes of Hg0 in the morning, (2) peak emissions near midafternoon, and (3) generally insignificant exchange during the nighttime. The fluxes of Hg over soil surfaces appear to be driven by a combined effect of several meteorological factors, including wind speed, vertical mixing, and soil temperature. Comparison of environmental conditions for both emission and deposition events showed that the direction of fluxes may be strongly influenced by the stability conditions of the boundary layer. The overall results of our emission and dry-deposition measurements in concern-with recent studies of wet-deposition rates in the forest ecosystem suggest that source strengths of this forest soil system may be of the same order of magnitude as sink strengths.
The Regional Lagrangian Model of Air Pollution (RELMAP) is used to simulate the emission, transport and diffusion, chemical transformation, and wet and dry deposition of elemental mercury gas, divalent mercury gas and particulate mercury. Based on recent modeling advances in Europe, the RELMAP has been modified to simulate a reduction-oxidation (redox) balance for mercury dissolved in cloud and rain water. This redox balance is used in the estimation of a variable precipitation scavenging ratio for elemental mercury. The results of the simulation are used to estimate the quantity of mercury emitted to the air annually over the United States and the amount that is subsequently deposited back to U.S. soils and water bodies. An analysis of the modeling results also provides some information about the areas of the country thought to have the most significant exposure from all air emissions of mercury.
This paper describes the development and application of the Visibility and Haze in the Western Atmosphere (VISHWA) model to understand the source-receptor relationships that govern chemical species relevant to visibility degradation in the western United States. The model was developed as part of a project referred to as Visibility Assessment for Regional Emission Distributions (VARED), the objective of which is to estimate the contributions of various geographical regions, compounds, and emissionsources to light scattering and absorption by particles on the Colorado Plateau.The VISHWA model is a modified version of a comprehensive Eulerian model, known as the Acid Deposition and Oxidant Model.1 The modifications were designed to obtain the computational efficiency required to simulate a one-year period at about 1/25th of real time, and at the same time incorporate mechanistic features relevant to realistic modeling of the fate and transport of visibility degrading species. The modifications included use of a condensed chemical mechanism; incorporation of reactions to simulate the formation of secondary organic particles; and use of a semi-Lagrangian advection scheme to preserve concentration peaks during advection.The model was evaluated with 1992 air quality data from Project MOHAVE (Measurements of Haze and Visual Effects) intensive experiments. An important conclusion of this evaluation is that aqueous-phase oxidation of SO2 to sulfate in nonprecipitating clouds makes a significant contribution to observed sulfate levels during winter as well as summer. Model estimates of ambient sulfatefor the winter intensive were within a factor of 2 of the observations for 75% of the values. The corresponding statistic for the summer intensive was 90%. Model estimates of carbon were within a factor of 2 of the limited set of observations.
The three components of the Regional Analysis and Forecast System (RAFS) of the National Meteorological Center (NMC) are described. This system was implemented in March 1985 to supplement guidance from NMC's limited-area fine-mesh model (LFM), especially for precipitation forecasting. The three components of the RAFS are the regional optimum interpolation analysis, the Baer–Tribbia nonlinear normal mode initialization, and the nested grid model—a grid point, primitive-equation model in sigma coordinates. Postprocessing of model forecasts and plans for system improvement are also discussed.
Surface soils collected near the Almadén, Spain, mercury mine reflected increasing concentrations of mercury (Hg) with proximity to the mine due to weathered mineral deposits and to atmospheric deposition of Hg from the smelter. Extractions with NaHCO3 or NH4OAc removed small amounts of Hg from both control (20 km from the mine; total Hg = 2.3 µg/g) and mine site soils (1 km; total Hg = 97 µg/g). Density gradient centrifugation indicated a significant fraction of the Hg to be associated with a high-density mineral fraction, presumably cinnabar. Accumulation of Hg by alfalfa suggested a dual mechanism of uptake; roots accumulated Hg in proportion to the soil levels, while aerial plant material absorbed Hg vapor directly from the atmosphere. Soil fertilization with and without liming significantly increased total Hg uptake, largely due to plant growth stimulation. Liming itself had no significant effect. The rate of volatilization of elemental Hg from both soils (∼0.13 and 0.33 µg/m² per hour at 25°C, for control and mine site, respectively) exceeded reported background emission rates by factors of 4 to 10, increasing with surface temperature and Hg content and decreasing with increased plant cover.
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Surface soils collected near the Almaden, Spain, mercury mine reflected increasing concentrations of mercury (Hg) with proximity to the mine due to weathered mineral deposits and to atmospheric deposition of Hg from the smelter. Extractions with NaHCOâ or NHâOAc removed small amounts of Hg from both control (20 km from the mine; total Hg = 2.3 ..mu..g/g) and mine site soils (1 km; total Hg = 97 ..mu..g/g). Density gradient centrifugation indicated a significant fraction of the Hg to be associated with a high-density mineral fraction, presumably cinnabar. Accumulation of Hg by alfalfa suggested a dual mechanism of uptake; roots accumulated Hg in proportion to the soil levels, while aerial plant material absorbed Hg vapor directly from the atmosphere. Soil fertilization with and without liming significantly increased total Hg uptake, largely due to plant growth stimulation. Liming itself had no significant effect. The rate of volatilization of elemental Hg from both soils (approx. 0.13 and 0.33 ..mu..g/m² per hour at 25°C, for control and mine site, respectively) exceeded reported background emission rates by factors of 4 to 10, increasing with surface temperature and Hg content and decreasing with increased plant cover.
This paper describes the development and evaluation of a comprehensive acid deposition model referred to as ADOM (Acid Deposition and Oxidant Model). The first part of the paper describes the general approach to the formulation of the model. The second part presents the evaluation of the model against observations collected during the OSCAR (April 1981) field study. Although the model performs well in explaining the magnitudes and variations of the observations, the discrepancies between model predictions and observations are not small. Because of the uncertainties in the data used to run and evaluate the model, these discrepancies do not necessarily suggest the need for modifications in the model. Therefore, we have supplemented the direct comparison of model predictions with observations with indirect methods that establish the correspondence between the model and reality. This paper describes one such technique that relies on the washout ratio, which is sometimes used to characterize scavenging of pollutants.
Aerosol and total vapor-phase Hg concentrations in air have been measured at Walker Branch Watershed, Tennessee for ≈ 2 yr.
Airborne Hg at this site is dominated by vapor forms which exhibit a strong seasonal cycle, with summer maxima that correspond
to elevated air temperature. Concentrations in this forest are near background levels; however, concentrations at a site within
3 km are significantly elevated due to emissions from Hg-contaminated soils. The concentration data have been combined with
a recently modified dry deposition model to estimate dry deposition fluxes to the deciduous forest at Walker Branch. Weekly
mean modeled Vd values for Hg° ranged from <0.01 (winter) to > 0.1 (summer) cm s1. Weekly dry deposition fluxes ranged from <0.1 µg m−2 during winter to > 1.0 µgg m−2 in the summer. Our dry deposition estimates plus limited measurements of wet deposition in this area indicate that dry deposition
may be the dominant input process in this forest, at least during the summer.
Atmospheric mobilization and exchange at the air-water interface are significant features of biogeochemical cycling of Hg
at the Earth's surface. Our marine studies of Hg have been extended to terrestrial aquatic systems, where we are investigating
the tropospheric cycling, deposition and air-water exchange of Hg in the mid-continental lacustrine environs of northcentral
Wisconsin. This program is part of a multidisciplinary examination into the processes regulating the aquatic biogeochemistry
of Hg in temperate regions. Trace-metal-free methodologies are employed to determine Hg and alkylated Hg species at the picomolar
level in air, water and precipitation. We have found Hg concentrations and atmospheric fluxes in these fresh water systems
to be similar to open ocean regions of the Northern Hemisphere. A well constrained mass balance for Hg has been developed
for one of the lakes, Little Rock Lake, which is an extensively studied clear water seepage lake that has been divided with
a sea curtain into two basins, one of which is untreated (reference pH: 6.1) while the other is being experimentally acidified
(current pH: 4.7). This budget shows that the measured total atmospheric Hg deposition (ca. 10 µg m−2 yr−1) readily accounts for the total mass of Hg in fish, water and accumulating in the sediments of Little Rock Lake. This analysis
demonstrates the importance of atmospheric Hg depositional fluxes to the geochemical cycling and bioaccumulation of Hg in
temperate lakes. It further suggests that modest increases in atmospheric Hg loading could lead directly to enhanced levels
of Hg in biota. Analogous modeling for monomethylmercury (MMHg) is as yet limited. Nevertheless, preliminary data for the
atmospheric deposition of MMHg indicate that this flux is insufficient. to account for the amounts of MMHg observed in biota.
An in-lake synthesis of MMHg is implicated. The importance of volatile Hg which is principally in the elemental form, and
its evasion to the atmosphere is also illustrated. We suggest that the in-lake production of Hg° can reduce the Hg (II) substrate
used in the in-lake microbiological synthesis of MMHg.
Measurements of Total Gaseous Mercury (TGM) in the atmosphere are being conducted as part of the Florida Atmospheric Mercury Study (FAMS). FAMS is a multi-year study focusing on the atmospheric transport and deposition of Hg and other trace metals at several locations in central and south Florida. A major component of this study, which this paper addresses, involves determining regional TGM concentrations and seasonal variability patterns at the various collection sites. Occasional problems were encountered in the collection efficiency of TGM on Au. The reason for this interference was not identified, but it was dramatically reduced by heating the collection columns to 80 C. Atmospheric Hg samples are currently being collected using Au-coated silica sand traps from atop 48 ft. aluminum sampling towers using an unattended and automated sampling and data recording system. We currently have approximately a two year record of TGM, beginning in the summer of 1992, for the Lake Barco Site, located in central Florida approximately 30 miles east of Gainesville, FL. The records at the south Florida sites are shorter, ranging from one month at Andytown to 16 months at both Fort Myers and Fakahatchee Strand. Average TGM concentrations (ng/m3) for 3 to 6 day integrated samples at the various sites are: Lake Barco, 1.590.58 (n=78); Fort Myers, 1.590.40 (n=42), Fakahatchee Strand, 1.420.41 (n=30); Tamiami Trail 1.460.80 (n=27); Everglades National Park 3.111.52 (n=13); and Andy Town, 1.780.62 (n=3). The mean Hg concentration for all the sites is 1.640.76 ng/m3 (n=191).
The atmospheric chemistry, deposition and transport of mercury (Hg) in the Upper Great Lakes region is being investigated at a near-remote sampling location in northern Wisconsin. Intensive sampling over two years and various seasons has been completed. A multi-phase collection strategy (gas-, particle- and precipitation-phases) was employed to gain insight into the processes controlling concentrations and chemical/physical speciation of atmospheric Hg. Additional chemical and physical atmospheric determinations (e.g. ozone, particulate constituents, meteorology) were also made during these periods to aid in the interpretation of the Hg determinations. For example, correlations of Hg with ozone, sulfur dioxide and synopticscale meteorological features suggest a regionally discernible signal in Hg. Comparison to isosigma backward air parcel trajectories confirms this regionality and implicates the areas south, southeast and northwest of the site to be sources for Hg. Particle-phase Hg (Hgp) was found to be approximately 40% in an oxidized form, or operationally defined as reactive. However, this was quite variable from year-to-year. Hgp and other particle constituents (esp. sulfate) show significant correlation and similarity in behavior (concentration ratios in precipitation and in particles). These observations are part of the growing evidence to support the hypothesis that precipitation-phase Hg arises in large part from the scavenging of atmospheric particulates bearing Hg. Observed concentrations of rain and particle-Hg fit broadly the theoretical expectations for nucleation and below-cloud scavenging. Significant increases in the Hg/aerosol mass ratio appear to take place during transport. Enrichment of aerosols is taken as evidence of gas/particle conversion which could represent the step linking gas-phase Hg with rain. The refined budget indicates ca. 24% of total deposition is from summer particle dry deposition, and that this deposition also contributes ca. 24% of all reactive Hg deposition. Additionally, almost all (86%) deposition (wet and dry) occurs during the summer months.
A reactive plume model that includes atmospheric chemical reactions of mercury was developed. The model simulates advective transport with the mean wind flow; horizontal and vertical turbulent diffusion; gas phase; aqueous-phase and particulate chemistry; cloud microphysics; wet deposition and dry deposition. The model was applied to the simulation of clear sky, non-precipitating cloud and precipitating cloud scenarios. No significant mercury chemistry occurs in the absence of droplets. In clouds, Hg(II) is reduced to Hg(0) with more reduction taking place in precipitating clouds than in non-precipitating clouds.
Estimates of mercury emissions from individual sources and source categories are needed to understand relationships between the emissions and resulting deposition and to evaluate possible approaches to reducing those emissions. We have developed geographically-resolved estimates of annual average mercury emission rates from current anthropogenic sources in the 48 contiguous United States. These estimates were made by applying emission factors to individual facility operating data and to county-wide source activity levels. We apportioned the emissions to an Eulerian modeling grid system using point source coordinates and the fractions of county areas in each grid cell. Point sources account for about 89% of the 48-state total mercury emissions of 146.4 Mg/yr. Most of the emissions in the inventory are from combustion of mercury-containing fossil fuels and municipal waste, located primarily in the mid-Atlantic and Great Lakes states as well as in the Southeast. The major uncertainties in the emission estimates are caused by uncertainties in the emission factors used to develop the estimates. This uncertainty is likely a result of variability in the mercury content of the combusted materials and in the removal of mercury by air pollution control devices. The greatest research need to reduce uncertainties in mercury emission estimates is additional measurements to improve emission factors.
Analysis of data collected during the Prairie Grass, Kansas and Minnesota experiments reveals the following empirical relationship between the Monin-Obukhov length L and the friction velocity u
*: L = Au
*
2, A = 1.1 103s2m-1. This result combined with the formulation for the height of the stable boundary layer h suggested by Zilitinkevich (1972) leads to h u
*
3/2
f–1/2 where f is the Coriolis parameter. Data from the Minnesota study (Caughey et al., 1979) provide ample support for this expression.These empirical equations for L and h are useful for routine dispersion estimates during stable conditions.
The Swedish Environmental Research Institute (IVL) in 1988 developed a passive sampler for collecting wetfall and some dryfall, which they have been using successfully in a network configuration for the past 4 years. The IVL, utilizing clean handling and analysis techniques (to avoid mercury contamination), has demonstrated that (for the locations being monitored) this modified bulk sampler can provide data comparable to wetfall-only sampling and integrated event sampling. It has been generally agreed that modified bulk sampling (such as the IVL sampler) was equivalent to wet-only sampling in areas not subject to large amounts of locally resuspended soil. Wisconsin has replicated the IVL sample (with some modifications and enhancements) and conducted a study of the feasibility of deploying a network of these passive modified bulk samplers. Triplicate samples were collected—on one purchased IVL and two Wisconsin-fabricated samplers—and analyzed for 17 weeks between mid-June and early October 1993. Comparison of rainfall volume in the IVL samplers versus the NADP Belfort rain gage (or the NADP Aerochem Metrics sampler) showed an average collection efficiency of 97% overall (with a few outliers). The average mercury concentration for all samples was 20.6 ng ℓ−1 with the median at 17.1 ng ℓ−1. The median weekly deposition rate of 0.226 μg m−2 yielded an extrapolated annual rate of 11.8 μ m−2, comparable to other reported data for the region. This paper presents details of the modified sampler, the results of the monitoring study, as well as some analysis of data.
A TDMA system (Tandem Differential Mobility Analyzer; Rader D.J. and McMurry P.H. J. Aerosol Sci. 17, 771–787, 1986) was used to measure the sensitivity of particle size to relative humidity for monodisperse Los Angeles aerosols. Measurements were made at Claremont, CA on 13 days between 19 June and 3 September 1987, in conjunction with the Southern California Air Quality Study (SCAQS). The particle sizes that were studied ranged from 0.05 μm to 0.5 μm diameter at ambient relative humidity (typically 45–65%).The data provide clear evidence that these atmospheric aerosols were externally mixed. Monodisperse ambient aerosols were often found to split into nonhygroscopic (no water uptake) and hygroscopic portions when humidified. An average of 30% of the particles in the 0.2–0.5 μm range were nonhygroscopic. However, the proportion of the particles that was nonhygroscopic varied considerably from day to day and was, on occasion, as high as 70–80% of the particles. There was no clear evidence for nonhygroscopic 0.05 μm particles, but the data are not definitive on this point.The data also show that for the hydrophilic aerosol fraction, the larger particles (0.4–0.5 μm) grew more when humidified than did smaller particles (0.05–0.2 μm). As relative humidities were increased from 50% to 90%, particle diameters grew by average factors of 1.46 ±0.02 (for 0.5 μm particles), 1.49 ± 0.08 (0.4 μm), 1.19 ± 0.08 (0.2 μm) and 1.12 ± 0.05 (0.05 μm). Similarly, when particles were dried from 50% RH to 6–10% RH, particle diameters changed by factors ranging from 0.94 ± 0.03 (0.5 μm) to 0.98 ± 0.01 (0.05 μm).
Regional patterns of seasonal and annual average air concentrations and cumulative deposition of mercury to the Great Lakes basin are calculated with the ASTRAP model. The model treats the Hg system as three chemical components: elemental (Hg0), particulate (Hg-p), and gaseous divalent (Hg-II). Primary anthropogenic emission inventories (i.e. emissions resulting from current activities) include surface and elevated sources of each of the three Hg species for eastern North America. Natural and secondary anthropogenic: emissions (i.e. reemission of Hg deposited or released during earlier anthropogenic activity) over the United States and Canada are estimated by defining an emission term for Hg' that varies with latitude and season. Global background concentrations of Hg0 and Hg-p are specified to average annually 1.0 and 0.01 ng m−3, respectively. Rates of parameterizations of wet and dry removal are very rapid for Hg-II, intermediate for Hg-p, and very slow for Hg0. Because of the disparate removal efficiencies, estimates of deposition resulting from anthropogenic emissions are critically dependent upon the speciation of emissions and, for the rapidly depositing Hg-II, the assumptions about effective stack heights. Integration of the Hg deposition field over the Great Lakes produces estimates of direct atmospheric loading from primary anthropogenic emissions of 1.44 and 2.46 t Hg yr−1 by wet and dry deposition, respectively. Estimates of direct loading from natural and secondary anthropogenic emissions of Hg0 over the continent are 0.09 and 0.15 t Hg yr−1 for wet and dry deposition, respectively, while the corresponding contributions from the global background are estimated to be 0.15 and 0.39 t Hg yr−1, respectively. Although they constitute only 16% of estimated anthropogenic emissions, emissions of Hg-II contribute 78% of the current direct anthropogenic deposition to the Lakes, or 65% of the deposition of Hg from all sources. Revolatilization of Hg0 from the Lakes is estimated to lie between 2.3 and 13.7 t Hg yr−1. Thus, revolatilization may well be greater than the direct atmospheric loading of all Hg species to the Lakes, 4.7 t Hg yr−1.
Most of the mercury contamination in lakes and streams of nonindustrialized regions of the United States, and Canada is derived from atmospheric deposition In order to determine the regional patterns of these inputs, seven mercury-in-precipitation monitoring sites were established in Minnesota, North Dakota, and Michigan. A 3-year study showed that the magnitude of mercury deposition was dominated by the quantity of precipitation. Regional variations of mercury concentrations in precipitation;were mostly explained by precipitation rate with higher concentrations occurring in the summer. Statewide (Minnesota) annual mercury emission estimates exceeded depositions for 1990, 1991, and 1992 by a factor of approximately 2 and indicated long-range transport of mercury. Significant correlations were observed between concentrations of mercury and other ions in precipitation.
The micrometerological modified Bowen ratio method was used for the first time to quantify fluxes of elemental mercury vapor (Hg[sup 0]) over contaminated soils during the spring and fall of 1993. We determined fluxes using relationships among the concentration gradients and fluxes of water vapor (measured with fast-response sensors and eddy correlation) and measured gradients in Hg[sup 0] (sampled with a multi-replicate, high-precision device). The contaminated soils consistently exhibited significant emission of Hg[sup 0] to the atmosphere. Fluxes associated with winds from the primary source area ranged from [approximately]10 to [approximately]200 ng m[sup [minus]2] h[sup [minus]1], up to several orders of magnitude above background. Fluxes increased exponentially with soil temperature, yielding a temperature coefficient similar to nitrogen oxide (exp[ T[sub soil]], for T[sub soil] = 7-29[degrees]C). These results provided confidence in the method for Hg[sup 0] because the gradients and fluxes behaved predictably. Fluxes appear to be controlled by volatilization of existing contaminant elemental Hg plus reduction of Hg[sup 2+] to Hg[sup 0] in soil solution. We modeled the emission from an area of contaminated soils within approximately 20-50 m of our site using the flux/soil temperature relationship and annual temperature data. 55 refs., 8 figs., 1 tab.
A chemical kinetic mechanism for the atmospheric chemistry of inorganic mercury has been developed. Computer simulations conducted with this mechanism suggest that the half-life of elemental mercury could be of the order of hours for reaction with Cl-2 in a nocturnal marine layer and for reactions with oxidants such as H2O2 in the ambient atmosphere. However, large uncertainties exist in the gasphase reaction rates of Hg(0) with Cl-2, O3, and H2O2, and the overall half-life of Hg(0) due to chemical reactions in the atmosphere cannot be assessed with certainty without further laboratory kinetic data. In the presence of an atmospheric liquid phase, oxidation and reduction reactions lead toward an equilibrium between Hg(0) and Hg(II). This equilibrium is a strong function of pH, liquid water content, and concentrations of SO2 and HCl. Under most simulation conditions, Hg(0) concentrations exceed Hg(II) concentrations by at least 1 order of magnitude, which is consistent with observations.
Thesis (Ph. D.)--University of London, 1980.
The “Great Waters” program, established in the 1990 Clean Air Act Amendments, mandated that atmospheric deposition of hazardous air pollutants to Lake Champlain (including Hg) be assessed. An assessment of the magnitude and seasonal variation of atmospheric Hg deposition in the Lake Champlain basin was initiated in December 1992 with one year of event precipitation collection, as well as collection of vapor and particle phase Hg in ambient air. Samples were collected at the Vermont Monitoring Cooperative air monitoring site at the Proctor Maple Research Center in Underhill Center, VT. The average volume-weighted concentration for Hg in precipitation was 8.3 ng/L for the sampling year and the average amount of Hg deposited with each precipitation event was 0.069 μg/m 2 . The total amount of Hg deposited through precipitation during 1993 was 9.26 μg/m 2 /yr. A seasonal pattern for Hg in precipitation was evident, with increased concentrations and deposition during spring and summer months. Meteorological analysis indicated the highest levels of Hg in precipitation were associated with regional transport from the south regardless of season, and with transport from the west, southwest and northwest during spring and summer months. Concentrations of ambient vapor phase Hg were typical of rural locations and consistent across seasons. Ambient particulate Hg concentrations averaged 11 pg/m 3 with highest concentrations during the winter months. Peer Reviewed http://deepblue.lib.umich.edu/bitstream/2027.42/43913/1/11270_2005_Article_BF01189685.pdf
To assess the sources, transport and deposition of atmospheric mercury (Hg) in Michigan, a multi-site network was implemented in which Hg concentrations in event precipitation and ambient samples (vapor and participate phases) were determined. Results from the analysis of 2 years of event precipitation samples for Hg are reported here. The volume-weighted average Hg concentration in precipitation was 7.9, 10.8 and 10.2 ng/L for the Pellston, South Haven and Dexter sites, respectively. Yearly wet deposition of Hg for 1992–93 and 1993–94 was 5.8 and 5.5 μg/m 2 at Pellston, 9.5 and 12.7 μg/m 2 at South Haven and 8.7 and 9.1 μg/m at Dexter. A spatial gradient in both the Hg concentration and wet deposition was observed. Northern Michigan received almost half the deposition of Hg recorded at the southern Michigan sites. The concentration of Hg in precipitation exhibited a strong seasonal behavior with low values of 1.0 to 2.0 ng/L in winter and maximum values greater than 40 ng/L in summer. The spring, summer and autumn precipitation accounted for 89 to 91% of the total yearly Hg deposition. Mixed-layer back trajectories were calculated for each precipitation event to investigate the meteorological history and transport from potential Hg source regions. Elevated Hg concentrations were observed with air mass transport from the west, southwest, south, and southeast. At each of the sites precipitation events for which the Hg concentration was in the 90th and 10th percentile were-analyzed for trace elements by ICP-MS to investigate source impacts. Peer Reviewed http://deepblue.lib.umich.edu/bitstream/2027.42/43912/1/11270_2005_Article_BF01189668.pdf
Development and testing of an urban grid model for the Santiago Chile region. In Air Pollution Modeling and its Application XI
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Karamchandani, P., Venkatram, A., Kashanian, K., Tubing, M. and Ulricksen, P. (1991) Development and testing of an urban grid model for the Santiago Chile region. In Air Pollution Modeling and its Application XI (edited by Han van Dop), pp. 169-IL76. Plenum Press, New York.
ADOM/TADAP model development program, vol-ume 4: the dry deposition module. ERT Document No. PB890-520, ENSR Consulting and Engineering Diagnostic wind field modeling for complex terrain: Model development and testing
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Pleim, J., Venkatram, A. and Yamartino, R. (1984) ADOM/TADAP model development program, vol-ume 4: the dry deposition module. ERT Document No. PB890-520, ENSR Consulting and Engineering, Acton, MA. Ross, D. G., Smith, I. N., Manins, P. C. and Fox, D. G. (1988) Diagnostic wind field modeling for complex terrain: Model development and testing. Journal of Applied Meteorology 27, 785-795.
Testing a comprehensive acid deposition model Atmospheric Environment 22 The development of a model to examine sourc~receptor relationships for vis-ibility on the Colorado plateau
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Uncertainties associated with source-receptor relationships for visibility reducing spe-cies derived from a j~,rid model. In Air Pollution Modeling and its Application XI (edited by Gryning S
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Karamchandani, P. and Pai, P. (1996) Uncertainties associated with source-receptor relationships for visibility reducing spe-cies derived from a j~,rid model. In Air Pollution Modeling and its Application XI (edited by Gryning S.-E. and Schiermeier F. A.), pp. 145-154. Plenum Press, New York.
Atmo-spheric mercury measurements in the Great Lakes basin: methods comparison and recent findings. In Mercury Pol-lution: Integration aJ~d Synthesis
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Keeler, G. E., Hoyer, M. E. and Lamborg, C. (1994) Atmo-spheric mercury measurements in the Great Lakes basin: methods comparison and recent findings. In Mercury Pol-lution: Integration aJ~d Synthesis (edited by Watras C. and Huckabee J.). Lewis Publishers, Boca Raton, FL.
Atmospheric mercury deposition in Ontario The modeling of regional-scale atmospheric mercury transport and deposition using RELMAP. Environmental Toxico-logy and Chemistry, in press Wet deposition and ambient mercury concentrations at a site in the Lake Champlain Basin
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Mixing heights, wind speeds, and potential for urban air pollution throughout the contiguous United States
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Air-water cycling of mercury in lakes
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Interim data interpretation report of the MIT/ALSC data set
- Olmez
Modeling of photochemical oxidant formation in North-Western Europe with special emphasis on the nonlinearity issue in the SOx/NOx/VOC system
- Stern
Laboratory studies of the reaction of gaseous elemental mercury (Hg0) with H202, 03, CH3I and (CH3)2S
- Tokos
Development and testing of dry deposition algorithms
- EPA
Mercury study report to congress: SAB review draft
- EPA