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Synoptic and Mesoscale Weather Conditions During Air Pollution Episodes in Athens, Greece
Abstract
Based on regular climatological and air quality data from the Greater Athens Area (GAA), the air pollution episodes observed
in Athens during the period 1983–1990 were analysed and classified. The main characteristics of atmospheric conditions during
days with high air pollution concentrations are summarized too. Model simulations show that the worst air pollution episodes
in Athens occur during days with a critical balance between synoptic and mesoscale circulations and/or during days with warm
advection in the lower troposphere.
... On the contrary, most of the industrial activity in the GAA is concentrated in the Thriassion Plain, 10-20 km to the northwest of Piraeus [41]. bined with weak northerlies or calms during the night [42,43]. Strong synoptic-scale N-NE advections are most frequent during winter over the GAA and blow over day and night, while in summer, the northern Etesian wind regime often prevails in the daytime. ...
... The effect of the sea/land breeze system from the Saronic Gulf cell is present throughout the year, but is far more prevalent in the summer, with strong onshore flows observed during the day (typically exceeding 6 m s −1 around noon), also exhibiting a large vertical extent. This daytime pattern is typically combined with weak northerlies or calms during the night [42,43]. Strong synoptic-scale N-NE advections are most frequent during winter over the GAA and blow over day and night, while in summer, the northern Etesian wind regime often prevails in the daytime. ...
Port cities are affected by a wide array of emissions, including those from the shipping, road transport, and residential sectors; therefore, the characterization and apportionment of such sources in a high temporal resolution is crucial. This study presents measurements of fine aerosol chemical composition in Piraeus, one of the largest European ports, during two monthly periods (winter vs. summer) in 2018–2019, using online instrumentation (Aerosol Chemical Speciation Monitor—ACSM, 7-λ aethalometer). PMF source apportionment was performed on the ACSM mass spectra to quantify organic aerosol (OA) components, while equivalent black carbon (BC) was decomposed to its fossil fuel combustion and biomass burning (BB) fractions. The combined traffic, shipping and, especially, residential emissions led to considerably elevated submicron aerosol levels (22.8 μg m−3) in winter, which frequently became episodic late at night under stagnant conditions. Carbonaceous compounds comprised the major portion of this submicron aerosol in winter, with mean OA and BC contributions of 61% (13.9 μg m−3) and 16% (3.7 μg m−3), respectively. The contribution of BB to BC concentrations was considerable and spatially uniform. OA related to BB emissions (fresh and processed) and hydrocarbon-like OA (from vehicular traffic and port-related fossil fuel emissions including shipping) accounted for 37% and 30% of OA, respectively. In summer, the average PM1 concentration was significantly lower (14.8 μg m−3) and less variable, especially for the components associated with secondary aerosols (such as OA and sulfate). The effect of the port sector was evident in summer and maintained BC concentrations at high levels (2.8 μg m−3), despite the absence of BB and improved atmospheric dispersion. Oxygenated components yielded over 70% of OA in summer, with the more oxidized secondary component of regional origin being dominant (41%) despite the intensity of local sources, in the Piraeus environment. In general, with respect to local sources that can be the target of mitigation policies, this work highlights the importance of port-related activities but also reveals the extensive wintertime impact of residential wood burning. While a separation of the BB source is feasible, more research is needed on how to disentangle the short-term effects of different fossil-fuel combustion sources.
... This clear seasonality over Athens has already been discussed in Skoulidou et al. (2021b), while the effect of local wind patterns can greatly influence the NO 2 levels sensed by both satellite and ground-based instrument. Air pollution in the region is defined by a combination of anthropogenic (traffic, industrial, seaport and airport) emissions (Pateraki et al., 2013) and meteorological conditions driven by strong winter temperature inversions and sea breeze circulation in the summer (Kallos et al., 1993). Athens is furthermore surrounded by mountains in the north, east and west, which, combined with the Saronic Gulf in the south, limits the dispersal of polluted air (Grivas et al., 2008). ...
... Meteorological factors such as wind direction and speed, temperature, relative humidity, and mixing height have a crucial role in PM transport, dispersion, and deposition in the atmosphere (Gao et al., 2019). In addition, elevated concentrations of air pollutants can be associated with specific microscale meteorological conditions affecting the air quality of an area (Kallos et al., 1993;Triantafyllou, 2001). The wind rose diagrams presented in Fig. 8 show the wind direction during the first study period (2010)(2011)(2012)(2013)(2014)(2015) and the observed PM 10 concentrations at the monitoring station in K. Komi for the background (Fig. 8a) and non-background (Fig. 8b) days. ...
... Sea breezes discharge air pollutants from coastal cities and suburbs to inland areas (Bonsang et al., 2001). This cycle facilitates the accumulation of pollutants and generation of secondary pollutants under the influence of photochemistry (Kallos et al., 1993;Kotroni et al., 1999;Liu & Chan, 2002). In recent years, improvements in the atmospheric environment have reduced the number of primary pollutants and mitigated the generation of secondary pollutants (Fig. 2). ...
Forest decline, which occurs in mountainous regions in many countries, may result from the effects of acid fog, ozone, or deposition of other pollutants. We observed wet deposition of air pollutants at different altitudes on Mt. Oyama, situated southwest of Tokyo, for 1994 until 2019. During this period, the domestic atmospheric environment was improved in Japan. The average concentration of air pollutants around all the sampling sites on Mt. Oyama decreased by 63.01%, 32.08%, 8.80%, and 39.73% for NH3, HCl, HNO3, and SO2, respectively. The volume weighted mean (VWM) pH values showed an increasing trend for bulk deposition (+0.70% y⁻¹), fog water (+2.58% y⁻¹), and throughfall (+2.60% y⁻¹). Stemflow also increased (cedar, +1.17% y⁻¹; fir, +0.82% y⁻¹), although it included organic acids dissolved from the stem and it primarily had a low VWM pH value. The overall pH value of the fog water increased at the site, although acidic fog was still observed. Comparing fog water between winter and summer, a significant increase in pH occurred in summer, whereas no change occurred in winter. In summer, the sources of pollutants at Mt. Oyama are mainly from mainland Japan, and the frequency of low-pH acidic fog decreased annually. In winter, Mt. Oyama was affected by transboundary pollution, and acid fog occasionally occurred. Improvements in the domestic atmospheric environment and control of transboundary pollution will provide better conditions for mountain ecology that are free from acidic pollutants.
... The impact of regional influences on visibility was investigated by using the back trajectory and synoptic pattern classification approach. Both these methods are widely used for air quality and visibility-related studies (e.g., Kallos et al., 1993;Baltaci et al., 2019;Aman et al., 2020;Duc et al., 2016;Chen et al., 2014;Wimolwattanapun et al., 2011;Pongkiatkul & Kim Oanh, 2007). The 120-h back-trajectories and their heights were calculated for each day during the study period using the Hybrid Single-Particle Lagrangian Integrated Trajectory Model (HYSPLIT) developed by the National Oceanic and Atmospheric Administration (NOAA) (Stein et al., 2015). ...
Visibility and aerosol optical depth (AOD) characterization, and their relationship with PM10 and local and synoptic meteorology, were studied for January–March in 2014 and 2015 over Bangkok. Visibility degradation intensifies in the dry season as compared to the wet season due to increase in PM10 and unfavorable meteorological conditions. The average visibility is lower in January and February as compared to the other months. Relatively higher AOD in March despite lower PM10 is attributed to the synergetic effect of moderate relative humidity, secondary aerosols, elevated aerosol layer due to summertime convection, and biomass burning. Larger variability in visibility and PM10 in winter months is due to more synoptic weather fluctuations while AOD shows similar variability for all months attributed partly to fires. Higher PM10 and moderate-to-high relative humidity cause lower visibility in the morning while it improves in afternoon as PM10 and relative humidity decrease. AOD is higher in the afternoon as compared to that in the morning and evening as it is less sensitive to diurnal change in aerosols and meteorology at the surface level. Visibility and AOD relationships with PM10 are dependent on relative humidity. Weaker winds lead to lower visibility, higher PM10, and higher AOD irrespective of wind direction. Stronger winds improve visibility and decrease PM10 for all directions while AOD is higher for all directions except eastern and northeastern. The back-trajectory results show that the transport of pollutant and moist air is coupled with the synoptic weather and influence visibility and AOD. Two low-visibility events were investigated. The first event is potentially caused by the combined effect of local emissions and their accumulation due to stagnant weather conditions, secondary aerosols, and forest fires in the nearby regions. The second event can be attributed to the local emission and fires in the nearby area with hygroscopic growth of aerosols due to moist air from the Gulf of Thailand. Based on these findings, some policy implications have also been given.
... It has been characterized as the meeting point of air masses coming from Europe, Africa, and Asia. The anthropogenic emissions of Europe, Balkans, and the Black Sea meet with natural emissions mainly from North Africa and the Sahara Desert (Kallos et al., 1993) as well as from biomass burning activities (Balis et al., 2003), increasing the air pollution levels of the area (Kanakidou et al., 2011;Lelieveld et al., 2002). Additionally, two megacities exist in the Eastern Mediterranean basin: The Greater Cairo area (GCA) (Egypt) at the south edge and the Greater Istanbul Area (GIA) (Turkey) at the north east edge, as well as several large urban centers like the Greater Athens area (GAA) in Greece Kanakidou et al., 2011). ...
The knowledge of the background air pollution is essential in order to implement abatement strategies for improving air quality. In the present study, a statistical clustering algorithm based on Hidden Markov Models (HMMs) was used to determine the background concentrations of PM10 and O3 at a coastal monitoring site in the Eastern Mediterranean by analyzing an eight-year period of air quality data, from 2011 to 2018. Time series of the deseasonalized daily average concentrations of PM10 and O3 and their diurnal amplitudes were applied to the model to identify the unobserved patterns or hidden states that define the pollution states of the two mentioned air pollutants. The pollution state characterized by the lowest daily average concentration and diurnal amplitudes defined the background pollution level and had the main interest in the current work. The findings revealed that during the studied period, 59% of the total daily PM10 values and 67% of the O3 values corresponded to the background pollution state and the average background concentrations were 14.3 ± 5.2 μg/m³ for PM10 and 48.4 ± 8.2 ppb for O3 respectively. In the case of PM10, anthropogenic activities and Saharan dust events, which define different pollution states, contribute in a decisive way to the PM10 load in the region and play a significant role in the observed annual PM10 levels. Additionally, in the case of O3, anthropogenic activities and regional pollution affect the background levels of the region mainly during summer months. The proposed method is a flexible tool with great potential for estimating the background levels of air pollutants at various monitoring stations.
... Meteorological parameters which can affect the way atmospheric pollutants change are including wind shear and direction, atmospheric vertical temperature structure, humidity, and solar radiation [12][13][14]. For example, the absence of wind with appropriate intensity and temperature inversion that prevents convective movements can cause the accumulation of atmospheric pollutants in the lower layers [15]. Due to the importance of this issue, many studies have been conducted on the relationship between meteorological conditions and atmospheric parameters with air pollution. ...
Introduction: Air pollution is one of the main problems of industrial and large cities like Tehran, due to its harmful effects, especially on human health.
Materials and methods: Based on the intensity and continuity of the standard air pollution index during 2004-2020 for 112 cases in Tehran, the principal component analysis method was applied in T-mode and clustering of days for similar 500hPa geopotential height changes were provided. The synoptic patterns leading to these different pollution cases were obtained.
Results: The study of the mentioned days shows the activity of five atmospheric patterns with the frequency of 47, 28, 12, 13, and 4%, respectively.
Conclusion: The first pattern happens during the cold season, associated with the simultaneous placement of the atmospheric ridge along with Siberian high-pressure system. The second group, which occurs mostly in summer and during late spring, is controlled with the predominant ozone pollutant. The main activity of the third pattern occurrences in summer and late spring, which is associated with the presence of monsoon Indian low-pressure on the southeastern regions in Iran. The fourth pattern, which occurs mostly in spring and autumn, associates with the establishment of dynamic low pressure in the western regions of Iran and Iraq, as well as the establishment of the thermal low-pressure system in the central part of the country. The last group is a local pattern that occurs due to the passage of the gust front and the shear of the wind field dust rise in the Tehran.
The impact of very wet soil and canopy temperatures on the surface sensible heat flux, and on related daytime boundary-layer properties is evaluated. For very wet soils, two winter situations are considered, related to significant changes in soil surface temperature: (1) due to weather perturbations at a given location, and (2) due to the climatological north-south temperature gradient. Analyses and scaling of the various boundary-layer properties, and soil surface fluxes affecting the sensible beat flux, have been made; related evaluations show that changes in the sensible heat flux at a given location by a factor of 2 to 3 due to temperature changes related to weather perturbations is not uncommon. These changes result in significant alterations in the boundary-layer depth; in the atmospheric boundary-layer warming; and in the break-up time of the nocturnal surface temperature inversion. Investigation of the impact of the winter latitudinal temperature gradient on the above characteristics indicated that the relative increase in very wet soil sensible heat flux, due to the climatological reduction in the surface temperature in northern latitudes, moderates to some extent its reduction due to the corresponding decrease in solar radiation. Numerical model simulations confirmed these analytical evaluations.In addition, the impact of synoptic temperature perturbations during the transition seasons (fall and spring) on canopy sensible heal fluxes, and the related boundary-layer characteristics mentioned above, was evaluated. Analogous features to those found for very wet soil surfaces occurred also for the canopy situations. Likewise, evaluations were also carried out to explore the impact of high midlatitude foreste areas on the boundary-layer characteristics during the winter as compared to those during the summer. Similar impacts were found in both seasons, regardless of the substantial difference in the daily total solar radiation.
The temporal variation of specific humidity during morning hours was evaluated by analytic and numerical model scaling as well as by observational means. The scaling quantified (i) the gradual increase in the shelter increase humidity as the surface temperatures inversion is eroded during the morning hours; (ii) the sharp decrease in the shelter specific humidity when the newly developed boundary layer merges with the previous day's elevated neutral layer. The relation of these patterns to the early-morning thermal stratification and the Bowen ratio was estimated. Observational data supported the general features suggested by the scaling evaluations. The applied significance of the presented specific-humidity patterns is outlined.
The present study provides a preliminary evaluation of mesoscale circulations forced by surface gradients of heating arising from irrigated areas adjacent to dry land, utilizing a combination of satellite, observational, and modeling approaches. The irrigated crop areas of northeast Colorado were chosen for the study. For the cases studied satellite surface infrared temperature data indicated a typical temperature contrast of approximately 10 K at noon, between the irrigated area and the adjacent dry land. Surface observations and aircraft measurements within the lower region of the atmospheric boundary layer indicated, in general, a significant temperature contrast and moisture difference, thereby implying a potential thermally driven circulation. The anticipated thermally induced flows, however, were reflected in the measurements only by modest changes in the wind speed and wind direction across the contrast location. It is suggested that the daytime, elevated, terrain-forced flow in the area, and the synoptic flow, combined to mask to varying degrees the thermally induced circulation due to the irrigated land-dry land area effect. Numerical model simulations which were carried out over the studied area support this hypothesis. In addition, the impact of the irrigated areas on the moisture within the boundary layer, as well as on potential convective cloud developments is discussed.
A two-dimensional hydrostatic model has been employed to simulate
sea-breeze circulations introduced by different-sized landmasses. The
following influences on the sea breeze are examined. 1) environmental
thermal stratification, 2) synoptic flow, and 3) latitude.In the
simulation of a strip of land with a width of 150 km, the maximum
sea-breeze convergence is much better developed than for other widths.
This maximum computed upward velocity occurred when two sea-breeze cells
from the two sides of the land merge together in the late afternoon.For
the experiments presented here, the sea breeze reached the strongest
vertical velocity (1.7 m s1) when the environmental vertical
gradient of potential temperature is 2.5°C km1 with a
land width of 150 km. With a very stable static stability, the sea
breeze is not well developed.When the sea breeze occurs at 20°N, its
intensity is the strongest, presumably because the solar insulation is
greatest at this latitude for the separate simulations. At 60°N the
Coriolis force produce a larger alongshore wind and the solar heating is
less, therefore, the intensity of the sea breeze is weaker.A nonzero
synoptic flow is not a favorable factor for the development of the
strongest merged sea breezes.
This paper describes some improvements to the Colorado State University mesoscale model. The model was generally accurate in simulating the winds, but failed to replicate the observed southeasterly flow from Los Angeles into the San Fernando Valley. The simulated surface winds were more accurate during the daytime than during the night, since the model did not reproduce the nocturnal winds' spatial variability. The model is a good predictor of mixing heights, which is an important variable in predicting pollutant concentrations, and successfully replicated observed daytime boundary layer averages of wind and potential temperature. -from Authors
In each surface grid element of the numerical model similar homogeneous land patches located at different places within the element are regrouped into subgrid classes. Then, for each one of the subgrid classes, a sophisticated micrometeorological model of the soil-plant-atmosphere system is applied to assess the surface temperature, humidity, and fluxes to the atmosphere. This parameterization was incorporated into a mesoscale numerical model to test the impact of subgrid-scale land surface heterogeneities on the development of local circulations. Where strong contrasts in total sensible heat flux are generated by land surface heterogeneities, circulations as strong as sea breezes may develop. -from Authors
We employ daytime radiosonde data to analyze boundary layer (BL) variability within the Los Angeles Basin for a case study day. The predominantly mesoscale forcing in the region produces large spatial and temporal variations in BL depth and vertically averaged BL virtual potential temperature and wind velocity. Particularly notable are the shallowing of BL depth—beginning in midmorning at the coast and in the early afternoon inland—and the afternoon decrease in BL potential temperature. The relative importance of terms in the BL continuity, thermodynamics, and momentum equations is evaluated; values for area-averaged entrainment velocity, surface heat flux, and mean BL pressure gradient force (PGF) are derived as residuals. Our budget equations are vertically integrated to the variable BL top and are thus more appropriate to investigations of BL variables than are equations integrated to a fixed height. Advection and divergence are shown to affect BL depth, heating, and acceleration significantly...