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Actinic flux, as well as aerosol chemical and op-tical properties, were measured aboard the NASA DC-8 air-craft during the ARCTAS (Arctic Research of the Compo-sition of the Troposphere from Aircraft and Satellites) mis-sion in Spring and Summer 2008. These measurements were used in a radiative transfer code to retrieve spectral (350– 550 nm) aeros...
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... schematic of the retrieval used in this work is shown in Fig. 1. A similar retrieval method was outlined in Corr et al. (2009). High resolution SSA values at 200 UV and visi- ble wavelengths were retrieved by comparing measured ac- tinic flux to those modeled as a function of SSA and the asymmetry parameter (g) using the 4-stream discrete ordi- nate solver of the Tropospheric Ultraviolet and ...
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We use retrievals of aerosol extinction from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard the CALIPSO satellite to examine the vertical, horizontal and temporal variability of tropospheric Arctic aerosols during the period 2006–2012. We develop an empirical method that takes into account the difference in sensitivity betwee...
The albedo and transmittance of melting, first-year Arctic sea ice were measured during two cruises of the Impacts of Climate on the Eco-Systems and Chemistry of the Arctic Pacific Environment (ICESCAPE) project during the summers of 2010 and 2011. Spectral measurements were made for both bare and ponded ice types at a total of 19 ice stations in t...
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... However, their samples included smoke from cropland and boreal forest fires, so these results are not specific to boreal forest fires. Corr et al. (2012) found enhanced absorption at UV wavelength compared to visible wavelength in long-range transported biomass burning plumes (ARC-TAS-A) and those from boreal forests in Canada (ARCTAS-B). Differences in wavelength dependence of absorption between ARCTAS-A/B were attributed to differences in plume age and OA/BC ratio from different biomass burning sources. ...
... Its warming effect is either ignored in climate models 9,10 or estimated with large uncertainties, with contributions varying by a factor of 10 between studies, ranging from $3% to >50% relative to the warming effect of black carbon (BC). [11][12][13][14][15][16][17] Biomass burning and fossil fuel combustion are major sources of primary BrC and precursors of secondary BrC. [18][19][20] Natural and anthropogenic activities of these emissions have been intensifying in the Arctic and surrounding regions, e.g., from wildfires in Siberia and North America [21][22][23] and from shipping and industrialization, 24,25 respectively. ...
... The high uncertainty in the estimation of BrC radiative forcing stems from both insufficient observations and shortcomings in modeling. Currently, observations of BrC in the Arctic are spatially limited, 12,13,[26][27][28][29] hindering representative assessment of its warming effect in the circum-Arctic. Furthermore, current models have often assumed that the absorption coefficient of BrC is independent of location 30,31 or parameterized the absorption of BrC as a function of the ratio of BC to organic aerosol in the source region, 32-34 rather than from direct measurements in the Arctic. ...
Rapid warming in the Arctic has a huge impact on the global environment. Atmospheric brown carbon (BrC) is one of the least understood and uncertain warming agents due to a scarcity of observations. Here, we performed direct observations of atmospheric BrC and quantified its light-absorbing properties during a 2-month circum-Arctic cruise in summer of 2017. Through observation-constrained modeling, we show that BrC, mainly originated from biomass burning in the mid- to high latitudes of the Northern Hemisphere (∼60%), can be a strong warming agent in the Arctic region, especially in the summer, with an average radiative forcing of ∼90 mW m⁻² (∼30% relative to black carbon). As climate change is projected to increase the frequency, intensity, and spread of wildfires, we expect BrC to play an increasing role in Arctic warming in the future.
... In addition to the difference in the chemical properties between BC and BrC, there are also differences between them in physical properties, for example, the wavelength-dependent property, which is generally described using the absorption Ångström exponent (AAE). Previous studies have revealed that BC absorbs solar radiation over a broad spectrum from ultraviolet to infrared wavelengths but with a weak dependence on wavelength, that is, a low AAE value of approximately 1, whereas the light absorption of BrC increase sharply from short visible to ultraviolet wavelengths and hence is characteristic of higher AAE values (Corr et al., 2012;Lack & Langridge, 2013;Laskin et al., 2015;Moosmüller et al., 2011). This difference in wavelength dependency between BC and BrC and the assumed uniform AAE value for BC (AAE BC ) have been widely used in previous studies to calculate the light absorption attributed to BrC, which could not be measured directly like the absorption coefficient of BC using online instruments due to the diverse sources and complex chemical compositions (Lack & Langridge, 2013). ...
... AAE BC is the AAE caused by BC particles and is commonly used as unity in previous studies (Lack & Cappa, 2010;Moosmüller et al., 2011;Zhu et al., 2017). However, most recent studies have revealed the important lensing effects caused by the non-BC matter coating on pure BC cores (Corr et al., 2012;Gyawali et al., 2009;Lack & Langridge, 2013;Lewis et al., 2008), which enhance the real AAE values more significantly and lead to +7% to −22% uncertainty for the attributed BC light absorption (Lack & Langridge, 2013). In this study, an improved AAE method adopted from Yuan et al. (2016) was used to calculate AAE BC values during the three campaigns. ...
The Tibetan Plateau (TP) has received wide scientific concern in recent decades owing to its important impacts on regional climatic and cryospheric changes, hydrological cycles, and environments. However, our understanding of the spatial distribution of the chemical and optical properties of aerosols is still limited based on prior single‐site observations. In this study, aerosol light absorptions from black carbon (BC) and brown carbon (BrC) were explored and compared among three remote TP sites, including Qomolangma Station (QOMS) on the southern TP, Nam Co Station (NamCo) on the central TP, and Waliguan Observatory on the northeastern TP. Although the aerosol mass concentration at QOMS was less than half of that at Waliguan, the light absorption coefficient of aerosols at QOMS was nearly 5 times higher than that at Waliguan, mainly as a result of more light‐absorbing carbonaceous aerosols on the southern TP due to long‐range transported biomass burning emissions. Specifically, BC dominated aerosol light absorption at all wavelengths, whereas BrC contributed ∼30% of the light absorption at 370 nm at QOMS and ∼20% at Waliguan and NamCo. A major contributor to BrC light absorption at QOMS was biomass burning‐related organic aerosols apportioned from aerosol mass spectrometry measurements. Understanding the significant regional differences in aerosol light absorption properties on the TP is useful for evaluating the regional climatic and environmental effects and validating the model results on aerosol radiative forcing.
... Single scattering albedo values in other regions for smoke particles varied as follows: 0.81-0.89 in Southern Africa (Magi et al., 2003) and 0.80-0.85 at mid-latitudes (Levine, 1991). In contrast, and pointing to the complexity of different types of wildfires and plume history, other reports of SSA from wildfire samples over North America ranged from 0.90 to 0.99 (e.g., Corr et al., 2012;Shingler et al., 2016), where the enhancement in scattering was attributed to aging. During SABOR, the higher SSAs come primarily from near-shore observations where weakly absorbing aerosols from local sources contribute more to the total amount of aerosols than farther offshore. ...
The Western North Atlantic Ocean (WNAO) and adjoining East Coast of North America are of great importance for atmospheric research and have been extensively studied for several decades. This broad region exhibits complex meteorological features and a wide range of conditions associated with gas and particulate species from many sources regionally and other continents. As Part 1 of a 2‐part paper series, this work characterizes quantities associated with atmospheric chemistry, including gases, aerosols, and wet deposition, by analyzing available satellite observations, ground‐based data, model simulations, and reanalysis products. Part 2 provides insight into the atmospheric circulation, boundary layer variability, three‐dimensional cloud structure, properties, and precipitation over the WNAO domain. Key results include spatial and seasonal differences in composition along the North American East Coast and over the WNAO associated with varying sources of smoke and dust and meteorological drivers such as temperature, moisture, and precipitation. Spatial and seasonal variations of tropospheric carbon monoxide and ozone highlight different pathways toward the accumulation of these species in the troposphere. Spatial distributions of speciated aerosol optical depth and vertical profiles of aerosol mass mixing ratios show a clear seasonal cycle highlighting the influence of different sources in addition to the impact of intercontinental transport. Analysis of long‐term climate model simulations of aerosol species and satellite observations of carbon monoxide confirm that there has been a significant decline in recent decades among anthropogenic constituents owing to regulatory activities.
... Previous measurements of fresh or transported BBA from forest fires in the Amazon, Siberia and North America reported a range of (2 %-9 %) for the average BC mass fractions of BBA (Kondo et al., 2011;Sahu et al., 2012;Artaxo et al., 2013;Allan et al., 2014;Morgan et al., 2020). Corresponding average dry SSA (at ∼ 550 nm) ranged from 0.88 to 0.97, using in situ measurements with the PSAP and nephelometer (Corr et al., 2012;Johnson et al., 2016;Laing et al., 2016). Compared with other BB-type regions, BBA during CLARIFY was richer in BC, with larger BC mass fraction and lower SSA. ...
Seasonal biomass burning (BB) from June to October in
central and southern Africa leads to absorbing aerosols being transported
over the South Atlantic Ocean every year and contributes significantly to
the regional climate forcing. The vertical distribution of submicron
aerosols and their properties were characterized over the remote southeast
Atlantic, using airborne in situ measurements made during the
CLoud-Aerosol-Radiation Interactions and Forcing for Year 2017
(CLARIFY-2017) campaign. BB aerosols emitted from flaming-controlled fires
were intensively observed in the region surrounding Ascension Island, in the
marine boundary layer (MBL) and free troposphere (FT) up to 5 km. We show
that the aerosols had undergone a significant ageing process during
> 7 d transit from source, as indicated by the highly oxidized
organic aerosol. The highly aged BB aerosols in the far-field CLARIFY region
were also especially rich in black carbon (BC), with relatively low single-scattering albedos (SSAs), compared with those from other BB transported
regions.
The column-weighted dry SSAs during CLARIFY were observed to be 0.85, 0.84
and 0.83 at 405, 550 and 658 nm respectively. We also found significant
vertical variation in the dry SSA, as a function of relative chemical
composition and size. The lowest SSA in the column was generally in the low
FT layer around 2000 m altitude (averages: 0.82, 0.81 and 0.79 at 405, 550
and 658 nm). This finding is important since it means that BB aerosols
across the southeast Atlantic region are more absorbing than currently
represented in climate models, implying that the radiative forcing from BB
may be more strongly positive than previously thought. Furthermore, in the
FT, average SSAs at 405, 550 and 658 nm increased to 0.87, 0.86 and 0.85
with altitude up to 5 km. This was associated with an enhanced inorganic
nitrate mass fraction and aerosol size, likely resulting from increased
partitioning of ammonium nitrate to the existing particles at higher
altitude with lower temperature and higher relative humidity. After
entrainment into the boundary layer (BL), aerosols were generally smaller in dry size than in
the FT and had a larger fraction of scattering material with resultant
higher average dry SSA, mostly due to marine emissions and aerosol removal
by drizzle. In the BL, the SSA decreased from the surface to the BL top,
with the highest SSA in the column observed near the surface. Our results
provide unique observational constraints on aerosol parameterizations used
in modelling regional radiation interactions over this important region. We
recommend that future work should consider the impact of this vertical
variability on climate models.
... OC compounds that are absorbing in the ultraviolet (UV) and short-visible wavelengths are colloquially known as BrC. The wavelength dependency of BrC aerosol absorption coefficients can be described by an absorption Ångström exponent (AAE) that is significantly greater than one (Chakrabarty et al., 2010;Corr et al., 2012;Kirchstetter et al., 2004;McNaughton et al., 2011;Moosmüller et al., 2011), whereas BC aerosol absorption coefficients are less wavelength-dependent (i.e., AAE ≈ 1) over the visible range and its periphery (Bergstrom et al., 2007;Moosmüller et al., 2009). The optical properties of BrC are described by the wavelength-dependent BrC complex refractive index m λ written as ...
Light-absorbing organic carbon aerosol – colloquially known as brown carbon (BrC) – is emitted from combustion processes and has a brownish or yellowish visual appearance, caused by enhanced light absorption at shorter visible and ultraviolet wavelengths (0.3 µm≲λ≲0.5 µm). Recently, optical properties of atmospheric BrC aerosols have become the topic of intense research, but little is known about how BrC deposition onto snow surfaces affects the spectral snow albedo, which can alter the resulting radiative forcing and in-snow photochemistry. Wildland fires in close proximity to the cryosphere, such as peatland fires that emit large quantities of BrC, are becoming more common at high latitudes, potentially affecting nearby snow and ice surfaces. In this study, we describe the artificial deposition of BrC aerosol with known optical, chemical, and physical properties onto the snow surface, and we monitor its spectral radiative impact and compare it directly to modeled values. First, using small-scale combustion of Alaskan peat, BrC aerosols were artificially deposited onto the snow surface. UV–Vis absorbance and total organic carbon (TOC) concentration of snow samples were measured for samples with and without artificial BrC deposition. These measurements were used to first derive a BrC (mass) specific absorption (m2 g−1) across the UV–Vis spectral range. We then estimate the imaginary part of the refractive index of deposited BrC aerosol using a volume mixing rule. Single-particle optical properties were calculated using Mie theory, and these values were used to show that the measured spectral snow albedo of snow with deposited BrC was in general agreement with modeled spectral snow albedo using calculated BrC optical properties. The instantaneous radiative forcing per unit mass of total organic carbon deposited to the ambient snowpack was found to be 1.23 (+0.14/-0.11) W m−2 per part per million (ppm). We estimate the same deposition onto a pure snowpack without light-absorbing impurities would have resulted in an instantaneous radiative forcing per unit mass of 2.68 (+0.27/-0.22) W m−2 per ppm of BrC deposited.
... Compared with past in situ measurements of aged biomass burning aerosol, SSA values over SWA (0.71-0.77 at 550 nm) are at the lower end of those reported worldwide (0.73-0.99 at 550 nm) (Magi et al., 2003;Reid et al., 2005;Johnson et al., 2008;Corr et al., 2012;Laing et al., 2016). This can be attributed in part to the high flaming versus smouldering conditions of African smoke producing more BC particles (Andreae and Merlet, 2001;Reid et al., 2005), which inherently have low SSA compared to other regions (Dubovick et al., 2002). ...
Southern West Africa (SWA) is an African pollution hotspot but a
relatively poorly sampled region of the world. We present an overview of
in situ aerosol optical measurements collected over SWA in June and July 2016 as
part as of the DACCIWA (Dynamics-Aerosol-Chemistry-Clouds Interactions in
West Africa) airborne campaign. The aircraft sampled a wide range of air
masses, including anthropogenic pollution plumes emitted from the coastal
cities, long-range transported biomass burning plumes from central and
southern Africa and dust plumes from the Sahara and Sahel region, as well as
mixtures of these plumes. The specific objective of this work is to
characterize the regional variability of the vertical distribution of
aerosol particles and their spectral optical properties (single scattering
albedo: SSA, asymmetry parameter, extinction mass efficiency, scattering
Ångström exponent and absorption Ångström exponent: AAE). The first
findings indicate that aerosol optical properties in the planetary boundary
layer were dominated by a widespread and persistent biomass burning loading
from the Southern Hemisphere. Despite a strong increase in aerosol number
concentration in air masses downwind of urban conglomerations, spectral
SSA were comparable to the background and showed signatures of the absorption
characteristics of biomass burning aerosols. In the free troposphere,
moderately to strongly absorbing aerosol layers, dominated by either dust or
biomass burning particles, occurred occasionally. In aerosol layers
dominated by mineral dust particles, SSA varied from 0.81 to 0.92 at 550 nm
depending on the variable proportion of anthropogenic pollution particles
externally mixed with the dust. For the layers dominated by biomass burning
particles, aerosol particles were significantly more light absorbing than
those previously measured in other areas (e.g. Amazonia, North America), with
SSA ranging from 0.71 to 0.77 at 550 nm. The variability of SSA was mainly
controlled by variations in aerosol composition rather than in aerosol size
distribution. Correspondingly, values of AAE ranged from 0.9 to 1.1, suggesting
that lens-coated black carbon particles were the dominant absorber in the
visible range for these biomass burning aerosols. Comparison with the literature
shows a consistent picture of increasing absorption enhancement of biomass
burning aerosol from emission to remote location and underscores that the
evolution of SSA occurred a long time after emission.
The results presented here build a fundamental basis of knowledge about the
aerosol optical properties observed over SWA during the monsoon season and
can be used in climate modelling studies and satellite retrievals. In
particular and regarding the very high absorbing properties of biomass
burning aerosols over SWA, our findings suggest that considering the effect
of internal mixing on absorption properties of black carbon particles in
climate models should help better assess the direct and semi-direct
radiative effects of biomass burning particles.
... Previous measurements of fresh or transported BBA from forest fires in the Amazon, Siberia and North America reported a range of (2 -9%) for the average BC mass fractions of BBA (Kondo et al., 2011;Sahu et al., 2012;Artaxo et al., 2013;Allan et al., 2014;Morgan et al., 2019). Corresponding average dry SSA (at ~550 nm) ranged from 0.88 to 0.97, using in-situ measurements with PSAP and nephelometer (Corr et al., 2012;Johnson et al., 2016;Laing et al., 2016). Compared with other BB-type regions, BBA during CLARIFY was richer in BC, with larger BC mass fraction and lower SSA. ...
Abstract. Seasonal biomass burning (BB) from June to October in central and southern Africa leads to absorbing aerosols being transported over the south Atlantic Ocean every year, and contributes significantly to the regional climate forcing. The vertical distribution of submicron aerosols and their properties were characterized over the remote southeast Atlantic for the first time, using airborne in-situ measurements made during the CLoud-Aerosol-Radiation Interactions and Forcing for Year 2017 (CLARIFY-2017) campaign. BB aerosols were intensively observed in the region surrounding Ascension Island, in the marine boundary layer (MBL) and free troposphere (FT) up to 5 km. We show that the aerosols had undergone a significant aging process during > 7 days transit from source, as indicated by highly oxidized organic aerosol and thickly coated black carbon (BC). The highly aged BB aerosols in the CLARIFY region were also especially rich in BC compared with those from other regions.
We also found significant vertical variation in the single scattering albedos (SSA) of these aerosols, as a function of relative chemical composition and size. The lowest SSA was generally in the low FT layer around 2000 m altitude (medians: 0.83 at 405 nm and 0.80 at 658 nm). This finding is important since it means that BB aerosols across the east Atlantic region are more absorbing than is currently represented in climate models. Furthermore, in the FT, we show that SSA increased with altitude and this was associated with an enhanced inorganic nitrate mass fraction and aerosol size. This likely results from increased partitioning to the existing particles at higher altitude with lower temperature and higher relative humidity. After entrainment into the BL, aerosols were generally smaller in size than were observed in the FT, and had a larger fraction of scattering material with resultant higher average dry SSA, mostly due to marine emissions and aerosol removal by drizzle. Our results provide unique observational constraints on aerosol parameterizations used in modelling regional radiation interactions over this important region. We recommend that future work should consider the impact of this vertical variability on climate models.
... The advantage of this method can avert interference from insoluble absorption material (e.g., black carbon) and supply a high-resolution spectrum over a wide wavelength coverage. Furthermore, it is favorable for characterization of BrC light-absorbing components by combing with other analytical techniques, such as mass spectrometry (MS) Corr et al., 2012;Satish et al., 2017). ...
To investigate the characteristics of atmospheric brown carbon (BrC) in the semiarid region of East Asia, PM2.5 and size-resolved particles in the urban atmosphere of Xi'an, inland China, during the winter and summer of 2017 were collected and analyzed for optical properties and chemical compositions. Methanol extracts (MeOH extracts) were more light-absorbing than water extracts (H2O extracts) in the optical wavelength of 300–600 nm and well correlated with nitrophenols, polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs (r > 0.78). The light absorptions (absλ=365 nm) of H2O extracts and MeOH extracts in winter were 28±16 and 49±32 M m−1, respectively, which are about 10 times higher than those in summer, mainly due to the enhanced emissions from biomass burning for house heating. Water-extracted BrC predominately occurred in the fine mode (
... Yu et al. (2019) reported the potential coating of BrC onto sulfate and soot cores for particles at 100 nm to 2 μm in Svalbard. The overall contribution of BrC to total spectral absorption was estimated >50% for two biomass burning plumes for upper (April) and lower (June) troposphere by an aircraft study in the Arctic (Corr et al., 2012). However, field characterization of the light absorbing properties and the sources of BrC is still very limited (Laskin et al., 2015;Xie et al., 2018). ...
Brown carbon (BrC) is a source of light absorbing aerosols. The Arctic is more sensitive to emissions of light absorbing aerosols than lower latitudes. Knowledge of BrC in a historical period is beneficial to understand its role in a changing climate. Here, we present measurement of water‐soluble BrC (WS‐BrC) for the Arctic aerosols during late winter‐late spring in 1991. Mass absorption coefficient (0.07 ± 0.04 M m–1) and efficiency (0.41 ± 0.21 m2 g–1) at 365 nm of WS‐BrC were lower than those in polluted urban and rural regions. WS‐BrC was mainly from biomass burning/combustion (dark winter to mid‐March) and marine sources connected with photochemical gas to particle conversion (after polar sunrise to June). Solar radiative absorption of WS‐BrC relative to elemental carbon was 5% on average in February to April and surged to 34% after mid‐May. This study helps in understanding the role of BrC in the Arctic climate.
