Airborne in situ measurements of aerosol size distributions and black carbon across the Indo-Gangetic Plain during SWAAMI–RAWEX

Abstract. During the combined South-West Asian Aerosol–Monsoon Interactions and Regional Aerosol Warming Experiment (SWAAMI–RAWEX), collocated airborne measurements of aerosol number–size distributions in the size (diameter) regime 0.5 to 20 µm and black carbon (BC) mass concentrations were made across the Indo-Gangetic Plain (IGP), for the first time, from three distinct locations, just prior to the onset of the Indian summer monsoon. These measurements provided an east–west transect of region-specific properties of aerosols as the environment transformed from mostly arid conditions of the western IGP (represented by Jodhpur, JDR) having dominance of natural aerosols to the central IGP (represented by Varanasi, VNS) having very high anthropogenic emissions, to the eastern IGP (represented by the coastal station Bhubaneswar, BBR) characterized by a mixture of the IGP outflow and marine aerosols. Despite these, the aerosol size distribution revealed an increase in coarse mode concentration and coarse mode mass fraction (fractional contribution to the total aerosol mass) with the increase in altitude across the entire IGP, especially above the well-mixed region. Consequently, both the mode radii and geometric mean radii of the size distributions showed an increase with altitude. However, near the surface and within the atmospheric boundary layer (ABL), the features were specific to the different subregions, with the highest coarse mode mass fraction (FMC∼72 %) in the western IGP and highest accumulation fraction in the central IGP with the eastern IGP in between. The elevated coarse mode fraction is attributed to mineral dust load arising from local production as well as due to advection from the west. This was further corroborated by data from the Cloud-Aerosol Transport System (CATS) on board the International Space Station (ISS), which also revealed that the vertical extent of dust aerosols reached as high as 5 km during this period. Mass concentrations of BC were moderate (∼1 µg m−3) with very little altitude variation up to 3.5 km, except over VNS where very high concentrations were seen near the surface and within the ABL. The BC-induced atmospheric heating rate was highest near the surface at VNS (∼0.81 K d−1), while showing an increasing pattern with altitude at BBR (∼0.35 K d−1 at the ceiling altitude).

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Air-borne in-situ measurements of aerosol size distributions and BC across the IGP during SWAAMI

10.5194/acp-2020-144 ◽

2020 ◽

Author(s):

Mukunda Madhab Gogoi ◽

Venugopalan Nair Jayachandran ◽

Aditya Vaishya ◽

Surendran Nair Suresh Babu ◽

Sreedharan Krishnakumari Satheesh ◽

...

Keyword(s):

Black Carbon ◽

Mass Fraction ◽

Geometric Mean ◽

Space Station ◽

Aerosol Size Distribution ◽

Size Distributions ◽

Coastal Station ◽

Coarse Mode ◽

Very High ◽

Mass Concentrations

Abstract. During the South-West Asian Aerosol Monsoon Interaction (SWAAMI) experiment, collocated air-borne measurements of aerosol number-size distributions in the size (diameter) regime 0.5 to 20 µm and black carbon (BC) mass concentrations were made across the Indo-Gangetic Plains (IGP), for the first time, from three distinct locations, just prior to the advent of Indian Summer Monsoon over the IGP. These measurements provided an east-west transect of region-specific properties of aerosols as the environment transformed from mostly-arid conditions of western IGP (represented by Jodhpur, JDR) having dominance of natural aerosols to the Central IGP (represented by Varanasi, VNS) having very high anthropogenic emissions, to the eastern IGP (represented by the coastal station Bhubaneswar, BBR) characterized by a mixture of the IGP outflow and marine aerosols. Despite these, the aerosol size distribution revealed an increase in coarse mode concentration and coarse mode mass-fraction (fractional contribution to the total aerosol mass) with increase in altitude across the entire IGP, especially above the well-mixed region. Consequently, both the mode radii and geometric mean radii of the size distributions showed an increase with altitude. However, near the surface and within the atmospheric boundary layer (ABL), the features were specific to the different sub-regions; with highest coarse mode mass fraction (FMC ~ 72 %) in the western IGP and highest accumulation fraction in the Central IGP with the eastern IGP coming in-between. The elevated coarse mode fraction is attributed to mineral dust load arising from local production as well as due to advection from the west. This was further corroborated by data from Cloud Aerosol Transportation System (CATS) onboard International Space Station (ISS), which also revealed that the vertical extent of dust aerosols reached as high as 5 km during this period. Mass concentrations of Black Carbon (BC) were moderate (~ 1 µg m−3) with very little altitude variation up to 3.5 km, except in the Central IGP (VNS) where very high concentrations were seen near the surface and within the ABL.

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Vertical and horizontal distribution of sub-micron aerosol chemical composition and physical characteristics across Northern India, during the pre-monsoon and monsoon seasons

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acp-2018-1109 ◽

2018 ◽

pp. 1-31

Author(s):

James Brooks ◽

James D. Allan ◽

Paul I. Williams ◽

Dantong Liu ◽

Cathryn Fox ◽

...

Keyword(s):

Black Carbon ◽

Total Mass ◽

Mass Concentration ◽

Monsoon Season ◽

Aerosol Layer ◽

Gangetic Plain ◽

Submicron Aerosol ◽

Aerosol Mass ◽

Indo Gangetic Plain ◽

Mass Concentrations

Abstract. The vertical distribution in the physical and chemical properties of submicron aerosol has been characterised across northern India for the first time using airborne in-situ measurements. This study focusses primarily on the Indo-Gangetic Plain, a low-lying area in the north of India which commonly experiences high aerosol mass concentrations prior to the monsoon season. Data presented are from the UK Facility for Airborne Atmospheric Measurements BAe-146 research aircraft that performed flights in the region during the 2016 pre-monsoon (11th and 12th June) and monsoon (30th June to 11th July) seasons. Inside the Indo-Gangetic Plain boundary layer, organic matter dominated the submicron aerosol mass (43&thinsp;%) followed by sulphate (29&thinsp;%), ammonium (14&thinsp;%), nitrate (7&thinsp;%) and black carbon (7&thinsp;%). However, outside the Indo-Gangetic Plain, sulphate was the dominant species contributing 44&thinsp;% to the total submicron aerosol mass in the boundary layer, followed by organic matter (30&thinsp;%), ammonium (14&thinsp;%), nitrate (6&thinsp;%) and black carbon (6&thinsp;%). Chlorine mass concentrations were negligible throughout the campaign. Black carbon mass concentrations were higher inside the Indo-Gangetic Plain (2&thinsp;µg/m3 std) compared to outside (1&thinsp;µg/m3 std). Nitrate appeared to be controlled by thermodynamic processes, with increased mass concentration in conditions of lower temperature and higher relative humidity. Increased mass and number concentrations were observed inside the Indo-Gangetic Plain and the aerosol was more absorbing in this region, whereas outside the Indo-Gangetic Plain the aerosol was larger in size and more scattering in nature, suggesting greater dust presence especially in northwest India. The aerosol composition remained largely similar as the monsoon season progressed, but the total aerosol mass concentrations decreased by ~&thinsp;50&thinsp;% as the rainfall arrived; the pre-monsoon average total mass concentration was 30&thinsp;µg/m3 std compared to a monsoon average total mass concentration of 10&ndash;20&thinsp;µg/m3 std. However, this mass concentration decrease was less noteworthy (~&thinsp;20&ndash;30&thinsp;%) over the Indo-Gangetic Plain, likely due to the strength of emission sources in this region. Decreases occurred in coarse mode aerosol, with the fine mode fraction increasing with monsoon arrival. In the aerosol vertical profile, inside the Indo-Gangetic Plain during the pre-monsoon, organic aerosol and absorbing aerosol species dominated in the lower atmosphere (<&thinsp;1.5&thinsp;km) with sulphate, dust and other scattering aerosol species enhanced in an elevated aerosol layer above 1.5&thinsp;km with maximum aerosol height ~&thinsp;6&thinsp;km. As the monsoon progressed into this region, the elevated aerosol layer diminished, the aerosol maximum height reduced to ~&thinsp;2&thinsp;km and the total mass concentrations decreased by ~&thinsp;50&thinsp;%. The dust and sulphate-dominated aerosol layer aloft was removed upon monsoon arrival, highlighted by an increase in fine mode fraction throughout the profile.

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Black Carbon and Elemental Carbon from Postharvest Agricultural-Waste Burning Emissions in the Indo-Gangetic Plain

Advances in Meteorology ◽

10.1155/2014/179301 ◽

2014 ◽

Vol 2014 ◽

pp. 1-10 ◽

Cited By ~ 25

Author(s):

Atinderpal Singh ◽

Prashant Rajput ◽

Deepti Sharma ◽

M. M. Sarin ◽

Darshan Singh

Keyword(s):

Black Carbon ◽

Elemental Carbon ◽

Agricultural Waste ◽

Absorption Efficiency ◽

High Mass ◽

Gangetic Plain ◽

Entire Study ◽

Waste Burning ◽

Indo Gangetic Plain ◽

Mass Concentrations

We compare the mass concentrations of black carbon (BC) and elemental carbon (EC) from different emissions in the Indo-Gangetic Plain (IGP), using optical (Aethalometer; 880 nm) and thermooptical technique (EC-OC analyzer; 678 nm), respectively. The fractional contribution of BC mass concentration measured at two different channels (370 and 880 nm), OC/EC ratio, and non-sea-salt K+/EC ratios have been systematically monitored for representing the source characteristics of BC and EC in this study. The mass concentrations of BC varied from 8.5 to 19.6, 2.4 to 18.2, and 2.2 to 9.4 μg m−3during October-November (paddy-residue burning emission), December–March (emission from bio- and fossil-fuel combustion) and April-May (wheat-residue burning emission), respectively. In contrast, the mass concentrations of EC varied from 3.8 to 17.5, 2.3 to 8.9, and 2.0 to 8.8 μg m−3during these emissions, respectively. The BC/EC ratios conspicuously greater than 1.0 have been observed during paddy-residue burning emissions associated with high mass concentrations of EC, OC, and OC/EC ratio. The Ångström exponent (α) derived from Aethalometer data is approximately 1.5 for the postharvest agricultural-waste burning emissions, hitherto unknown for the IGP. The mass absorption efficiency (MAE) of BC and EC centers at ~1–4 m2 g−1and 2-3 m2 g−1during the entire study period in the IGP.

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Vertical and horizontal distribution of submicron aerosol chemical composition and physical characteristics across northern India during pre-monsoon and monsoon seasons

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-5615-2019 ◽

2019 ◽

Vol 19 (8) ◽

pp. 5615-5634 ◽

Cited By ~ 19

Author(s):

James Brooks ◽

James D. Allan ◽

Paul I. Williams ◽

Dantong Liu ◽

Cathryn Fox ◽

...

Keyword(s):

Black Carbon ◽

Mass Concentration ◽

Monsoon Season ◽

Western India ◽

Aerosol Layer ◽

Gangetic Plain ◽

Submicron Aerosol ◽

Aerosol Mass ◽

Indo Gangetic Plain ◽

Mass Concentrations

Abstract. The vertical distribution in the physical and chemical properties of submicron aerosol has been characterised across northern India for the first time using airborne in situ measurements. This study focusses primarily on the Indo-Gangetic Plain, a low-lying area in the north of India which commonly experiences high aerosol mass concentrations prior to the monsoon season. Data presented are from the UK Facility for Airborne Atmospheric Measurements BAe-146 research aircraft that performed flights in the region during the 2016 pre-monsoon (11 and 12 June) and monsoon (30 June to 11 July) seasons. Inside the Indo-Gangetic Plain boundary layer, organic matter dominated the submicron aerosol mass (43&thinsp;%) followed by sulfate (29&thinsp;%), ammonium (14&thinsp;%), nitrate (7&thinsp;%) and black carbon (7&thinsp;%). However, outside the Indo-Gangetic Plain, sulfate was the dominant species, contributing 44&thinsp;% to the total submicron aerosol mass in the boundary layer, followed by organic matter (30&thinsp;%), ammonium (14&thinsp;%), nitrate (6&thinsp;%) and black carbon (6&thinsp;%). Chlorine mass concentrations were negligible throughout the campaign. Black carbon mass concentrations were higher inside the Indo-Gangetic Plain (2&thinsp;µg&thinsp;m−3) compared to outside (1&thinsp;µg&thinsp;m−3). Nitrate appeared to be controlled by thermodynamic processes, with increased mass concentration in conditions of lower temperature and higher relative humidity. Increased mass and number concentrations were observed inside the Indo-Gangetic Plain and the aerosol was more absorbing in this region, whereas outside the Indo-Gangetic Plain the aerosol was larger in size and more scattered in nature, suggesting greater dust presence, especially in north-western India. The aerosol composition remained largely similar as the monsoon season progressed, but the total aerosol mass concentrations decreased by ∼50&thinsp;% as the rainfall arrived; the pre-monsoon average total mass concentration was 30&thinsp;µg&thinsp;m−3 compared to a monsoon average total mass concentration of 10–20&thinsp;µg&thinsp;m−3. However, this mass concentration decrease was less noteworthy (∼20&thinsp;%–30&thinsp;%) over the Indo-Gangetic Plain, likely due to the strength of emission sources in this region. Decreases occurred in coarse mode aerosol, with the fine mode fraction increasing with monsoon arrival. In the aerosol vertical profile, inside the Indo-Gangetic Plain during the pre-monsoon, organic aerosol and absorbing aerosol species dominated in the lower atmosphere (&lt;1.5&thinsp;km), with sulfate, dust and other scattering aerosol species enhanced in an elevated aerosol layer above 1.5&thinsp;km with maximum aerosol height ∼6&thinsp;km. The elevated concentration of dust at altitudes &gt;1.5&thinsp;km is a clear indication of dust transport from the Great Indian Desert, also called the Thar Desert, in north-western India. As the monsoon progressed into this region, the elevated aerosol layer diminished, the aerosol maximum height reduced to ∼2&thinsp;km. The dust and sulfate-dominated aerosol layer aloft was removed upon monsoon arrival, highlighted by an increase in fine mode fraction throughout the profile.

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Wintertime direct radiative effects due to black carbon (BC) over the Indo-Gangetic Plain as modelled with new BC emission inventories in CHIMERE

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-7671-2021 ◽

2021 ◽

Vol 21 (10) ◽

pp. 7671-7694

Author(s):

Sanhita Ghosh ◽

Shubha Verma ◽

Jayanarayanan Kuttippurath ◽

Laurent Menut

Keyword(s):

Black Carbon ◽

Transport Model ◽

Eastern Coast ◽

Emission Inventories ◽

Surface Cooling ◽

Gangetic Plain ◽

Bottom Up ◽

Bc Aerosols ◽

Radiative Perturbation ◽

Indo Gangetic Plain

Abstract. To reduce the uncertainty in climatic impacts induced by black carbon (BC) from global and regional aerosol–climate model simulations, it is a foremost requirement to improve the prediction of modelled BC distribution, specifically over the regions where the atmosphere is loaded with a large amount of BC, e.g. the Indo-Gangetic Plain (IGP) in the Indian subcontinent. Here we examine the wintertime direct radiative perturbation due to BC with an efficiently modelled BC distribution over the IGP in a high-resolution (0.1∘ × 0.1∘) chemical transport model, CHIMERE, implementing new BC emission inventories. The model efficiency in simulating the observed BC distribution was assessed by executing five simulations: Constrained and bottomup (bottomup includes Smog, Cmip, Edgar, and Pku). These simulations respectively implement the recently estimated India-based observationally constrained BC emissions (Constrainedemiss) and the latest bottom-up BC emissions (India-based: Smog-India; global: Coupled Model Intercomparison Project phase 6 – CMIP6, Emission Database for Global Atmospheric Research-V4 – EDGAR-V4, and Peking University BC Inventory – PKU). The mean BC emission flux from the five BC emission inventory databases was found to be considerably high (450–1000 kg km−2 yr−1) over most of the IGP, with this being the highest (> 2500 kg km−2 yr−1) over megacities (Kolkata and Delhi). A low estimated value of the normalised mean bias (NMB) and root mean square error (RMSE) from the Constrained estimated BC concentration (NMB: < 17 %) and aerosol optical depth due to BC (BC-AOD) (NMB: 11 %) indicated that simulations with Constrainedemiss BC emissions in CHIMERE could simulate the distribution of BC pollution over the IGP more efficiently than with bottom-up emissions. The high BC pollution covering the IGP region comprised a wintertime all-day (daytime) mean BC concentration and BC-AOD respectively in the range 14–25 µg m−3 (6–8 µg m−3) and 0.04–0.08 µg m−3 from the Constrained simulation. The simulated BC concentration and BC-AOD were inferred to be primarily sensitive to the change in BC emission strength over most of the IGP (including the megacity of Kolkata), but also to the transport of BC aerosols over megacity Delhi. Five main hotspot locations were identified in and around Delhi (northern IGP), Prayagraj–Allahabad–Varanasi (central IGP), Patna–Palamu (upper, lower, and mideastern IGP), and Kolkata (eastern IGP). The wintertime direct radiative perturbation due to BC aerosols from the Constrained simulation estimated the atmospheric radiative warming (+30 to +50 W m−2) to be about 50 %–70 % larger than the surface cooling. A widespread enhancement in atmospheric radiative warming due to BC by 2–3 times and a reduction in surface cooling by 10 %–20 %, with net warming at the top of the atmosphere (TOA) of 10–15 W m−2, were noticed compared to the atmosphere without BC, for which a net cooling at the TOA was exhibited. These perturbations were the strongest around megacities (Kolkata and Delhi), extended to the eastern coast, and were inferred to be 30 %–50% lower from the bottomup than the Constrained simulation.

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Long-term observations of tropospheric particle number size distributions and equivalent black carbon mass concentrations in the German Ultrafine Aerosol Network (GUAN)

Earth System Science Data ◽

10.5194/essd-8-355-2016 ◽

2016 ◽

Vol 8 (2) ◽

pp. 355-382 ◽

Cited By ~ 30

Author(s):

Wolfram Birmili ◽

Kay Weinhold ◽

Fabian Rasch ◽

André Sonntag ◽

Jia Sun ◽

...

Keyword(s):

Black Carbon ◽

Particle Number ◽

Measurement Data ◽

Urban Traffic ◽

Data Evaluation ◽

Size Distributions ◽

Evaluation Procedures ◽

Carbon Mass ◽

Ultrafine Aerosol ◽

Mass Concentrations

Abstract. The German Ultrafine Aerosol Network (GUAN) is a cooperative atmospheric observation network, which aims at improving the scientific understanding of aerosol-related effects in the troposphere. The network addresses research questions dedicated to both climate- and health-related effects. GUAN's core activity has been the continuous collection of tropospheric particle number size distributions and black carbon mass concentrations at 17 observation sites in Germany. These sites cover various environmental settings including urban traffic, urban background, rural background, and Alpine mountains. In association with partner projects, GUAN has implemented a high degree of harmonisation of instrumentation, operating procedures, and data evaluation procedures. The quality of the measurement data is assured by laboratory intercomparisons as well as on-site comparisons with reference instruments. This paper describes the measurement sites, instrumentation, quality assurance, and data evaluation procedures in the network as well as the EBAS repository, where the data sets can be obtained (doi:10.5072/guan).

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Black Carbon physical and optical properties across northern India during pre-monsoon and monsoon seasons

10.5194/acp-2019-505 ◽

2019 ◽

Author(s):

James Brooks ◽

Dantong Liu ◽

James D. Allan ◽

Paul I. Williams ◽

Jim Haywood ◽

...

Keyword(s):

Physical Properties ◽

Black Carbon ◽

Mixing State ◽

Atmospheric Measurements ◽

Core Diameter ◽

Gangetic Plain ◽

North West ◽

North East ◽

Northern India ◽

Indo Gangetic Plain

Abstract. Black carbon (BC) is known to have major impacts on both climate and human health, so is therefore of global importance, particularly so in regions close to large populations that have strong sources. The physical properties and mixing state of black carbon containing particles are important determinants in these effects but information is often lacking, particularly in some of the most important regions of the globe. Detailed analysis into the vertical and horizontal BC optical and physical properties across northern India has been carried out using airborne in-situ measurements. The size-resolved mixing state of BC-containing particles was characterised using a single particle soot photometer (SP2). The study focusses on the Indo-Gangetic Plain during the pre-monsoon and monsoon seasons. Data presented are from the UK Facility for Airborne Atmospheric Measurements BAe-146 research aircraft that performed flights during the pre-monsoon (11th and 12th June) and monsoon (30th June to 11th July) seasons of 2016. Over the Indo-Gangetic Plain, BC mass concentrations were greater (1.95 µg/m3) compared to north-west India (1.50 µg/m3) and north-east India (0.70 µg/m3) during the pre-monsoon. Across northern India, two distinct BC modes were recorded; a mode of small BC particles (core diameter

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Evaluation of emission strength efficacy in simulating black carbon burden with CHIMERE: estimating wintertime radiative effect over Indo-Gangetic Plain

10.5194/egusphere-egu2020-17436 ◽

2020 ◽

Author(s):

Sanhita Ghosh ◽

Shubha Verma ◽

Jayanarayanan Kuttippurath

Keyword(s):

Black Carbon ◽

Transport Model ◽

Indian Subcontinent ◽

Chemical Transport ◽

Climate Impacts ◽

Eastern Coast ◽

Spatial And Temporal Patterns ◽

Gangetic Plain ◽

Bc Aerosols ◽

Indo Gangetic Plain

Black carbon (BC) aerosols over the Indian subcontinent have been represented inadequately so-far in chemical transport models restricting the accurate assessment of BC-induced climate impacts. The divergence between simulated and measured BC concentration has specifically been reported to be large over the Indo-Gangetic Plain (IGP) during winter when a large BC burden is observed. In this study, we evaluate the BC transport simulations over the IGP in a high resolution (0.1&#186; &#215; 0.1&#186; ) chemical transport model, CHIMERE. We examine the model efficiency to simulate the observed BC distribution executing five sets of simulation experiments: Constrained and bottomup (Smog, Pku, Edgar, Cmip) implementing respectively, the recently estimated India-based constrained BC emission and the latest bottom-up BC emissions (India-based: Smog-India, and global: Coupled Model Intercomparison Project phase 6 (CMIP6), Emission Database for Global Atmospheric Research-V4 (EDGAR-V4) and Peking University BC Inventory (PKU)). The mean BC emission flux over most of the IGP from the five emission datasets is considerably high (450&#8211;1000 kg km-2 y-1) with a relatively low divergence obtained for the eastern and upper-mideastern IGP. Evaluation of BC transport simulations shows that the spatial and temporal gradient in the simulated BC concentration from the Constrained was equivalent to that from the bottomup and also to that from observations. This indicates that the spatial and temporal patterns of BC concentration are consistently simulated by the model processes. However, the efficacy to simulate BC distribution is commendable for the estimates from Constrained for which the lowest normalised mean bias (NMB, < 20%) is obtained in comparison to that from the bottomup (37&#8211;52%). 75&#8211;100% of the observed all-day (daytime) mean BC concentration is simulated most of the times (>80% of the number of stations data) for Constrained, whereas, this being less frequent (<50%) for the Pku, Smog, Edgar and poor for Cmip. The BC-AOD (0.04&#8211;0.08) estimated from the Constrained is 20&#8211;50% higher than the Pku and Smog. Three main hotspot locations comprising of a large value of BC load are identified over the eastern, mideastern, and northern IGP. Assessment of the effect of BC burden on the wintertime radiative perturbation over the IGP shows that the presence of BC aerosols in the atmosphere enhances atmospheric heating by 2&#8211;3 times more compared to that considering atmosphere without BC. Also, a net warming at the top of the atmosphere (TOA) by 10&#8211;17 W m-2 is noticed from the Constrained, with the largest value estimated in and around megacities (Kolkata and Delhi) that extends to the eastern coast. This value is higher by 10&#8211;20% than that from Cmip over the IGP and by 2&#8211;10% than that from Smog over Delhi and eastern part of the IGP.

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A global 3-D CTM evaluation of black carbon in the Tibetan Plateau

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-7091-2014 ◽

2014 ◽

Vol 14 (13) ◽

pp. 7091-7112 ◽

Cited By ~ 30

Author(s):

C. He ◽

Q. B. Li ◽

K. N. Liou ◽

J. Zhang ◽

L. Qi ◽

...

Keyword(s):

Tibetan Plateau ◽

Black Carbon ◽

Transport Model ◽

The Tibetan Plateau ◽

Emission Inventories ◽

Chemical Transport Model ◽

Central Plateau ◽

Gangetic Plain ◽

Rural Sites ◽

Indo Gangetic Plain

Abstract. We systematically evaluate the black carbon (BC) simulations for 2006 over the Tibetan Plateau by a global 3-D chemical transport model (CTM) (GEOS-Chem) driven by GEOS-5 assimilated meteorological fields, using in situ measurements of BC in surface air, BC in snow, and BC absorption aerosol optical depth (AAOD). Using improved anthropogenic BC emission inventories for Asia that account for rapid technology renewal and energy consumption growth (Zhang et al., 2009; Lu et al., 2011) and improved global biomass burning emission inventories that account for small fires (van der Werf et al., 2010; Randerson et al., 2012), we find that model results of both BC in surface air and in snow are statistically in good agreement with observations (biases < 15%) away from urban centers. Model results capture the seasonal variations of the surface BC concentrations at rural sites in the Indo-Gangetic Plain, but the observed elevated values in winter are absent. Modeled surface-BC concentrations are within a factor of 2 of the observations at remote sites. Part of the discrepancy is explained by the deficiencies of the meteorological fields over the complex Tibetan terrain. We find that BC concentrations in snow computed from modeled BC deposition and GEOS-5 precipitation are spatiotemporally consistent with observations (r = 0.85). The computed BC concentrations in snow are a factor of 2–4 higher than the observations at several Himalayan sites because of excessive BC deposition. The BC concentrations in snow are biased low by a factor of 2 in the central plateau, which we attribute to the absence of snow aging in the CTM and strong local emissions unaccounted for in the emission inventories. Modeled BC AAOD is more than a factor of 2 lower than observations at most sites, particularly to the northwest of the plateau and along the southern slopes of the Himalayas in winter and spring, which is attributable in large part to underestimated emissions and the assumption of external mixing of BC aerosols in the model. We find that assuming a 50% increase of BC absorption associated with internal mixing reduces the bias in modeled BC AAOD by 57% in the Indo-Gangetic Plain and the northeastern plateau and to the northeast of the plateau, and by 16% along the southern slopes of the Himalayas and to the northwest of the plateau. Both surface BC concentration and AAOD are strongly sensitive to anthropogenic emissions (from China and India), while BC concentration in snow is especially responsive to the treatment of BC aerosol aging. We find that a finer model resolution (0.5° × 0.667° nested over Asia) reduces the bias in modeled surface-BC concentration from 15 to 2%. The large range and non-homogeneity of discrepancies between model results and observations of BC across the Tibetan Plateau undoubtedly undermine current assessments of the climatic and hydrological impact of BC in the region and thus warrant imperative needs for more extensive measurements of BC, including its concentration in surface air and snow, AAOD, vertical profile and deposition.

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