Quantifying sources, transport, deposition, and radiative forcing of black carbon over the Himalayas and Tibetan Plateau

Abstract. Black carbon (BC) particles over the Himalayas and Tibetan Plateau (HTP), both airborne and those deposited on snow, have been shown to affect snowmelt and glacier retreat. Since BC over the HTP may originate from a variety of geographical regions and emission sectors, it is essential to quantify the source–receptor relationships of BC in order to understand the contributions of natural and anthropogenic emissions and provide guidance for potential mitigation actions. In this study, we use the Community Atmosphere Model version 5 (CAM5) with a newly developed source-tagging technique, nudged towards the MERRA meteorological reanalysis, to characterize the fate of BC particles emitted from various geographical regions and sectors. Evaluated against observations over the HTP and surrounding regions, the model simulation shows a good agreement in the seasonal variation in the near-surface airborne BC concentrations, providing confidence to use this modeling framework for characterizing BC source–receptor relationships. Our analysis shows that the relative contributions from different geographical regions and source sectors depend on season and location in the HTP. The largest contribution to annual mean BC burden and surface deposition in the entire HTP region is from biofuel and biomass (BB) emissions in South Asia, followed by fossil fuel (FF) emissions from South Asia, then FF from East Asia. The same roles hold for all the seasonal means except for the summer, when East Asia FF becomes more important. For finer receptor regions of interest, South Asia BB and FF have the largest impact on BC in the Himalayas and central Tibetan Plateau, while East Asia FF and BB contribute the most to the northeast plateau in all seasons and southeast plateau in the summer. Central Asia and Middle East FF emissions have relatively more important contributions to BC reaching the northwest plateau, especially in the summer. Although local emissions only contribute about 10% of BC in the HTP, this contribution is extremely sensitive to local emission changes. Lastly, we show that the annual mean radiative forcing (0.42 W m−2) due to BC in snow outweighs the BC dimming effect (−0.3 W m−2) at the surface over the HTP. We also find strong seasonal and spatial variation with a peak value of 5 W m−2 in the spring over the northwest plateau. Such a large forcing of BC in snow is sufficient to cause earlier snow melting and potentially contribute to the acceleration of glacier retreat.

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Quantifying sources, transport, deposition and radiative forcing of black carbon over the Himalayas and Tibetan Plateau

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-77-2015 ◽

2015 ◽

Vol 15 (1) ◽

pp. 77-121 ◽

Cited By ~ 3

Author(s):

R. Zhang ◽

H. Wang ◽

Y. Qian ◽

P. J. Rasch ◽

R. C. Easter ◽

...

Keyword(s):

Tibetan Plateau ◽

East Asia ◽

South Asia ◽

Black Carbon ◽

Radiative Forcing ◽

Glacier Retreat ◽

Modeling Framework ◽

Near Surface ◽

Geographical Regions ◽

Source Receptor Relationships

Abstract. Black carbon (BC) particles over the Himalayas and Tibetan Plateau (HTP), both airborne and those deposited on snow, have been shown to affect snowmelt and glacier retreat. Since BC over the HTP may originate from a variety of geographical regions and emission sectors, it is essential to quantify the source–receptor relationships of BC in order to understand the contributions of natural and anthropogenic emissions and provide guidance for potential mitigation actions. In this study, we use the Community Atmosphere Model version 5 (CAM5) with a newly developed source tagging technique, nudged towards the MERRA meteorological reanalysis, to characterize the fate of BC particles emitted from various geographical regions and sectors. Evaluated against observations over the HTP and surrounding regions, the model simulation shows a good agreement in the seasonal variation of the near-surface airborne BC concentrations, providing confidence to use this modeling framework for characterizing BC source–receptor relationships. Our analysis shows that the relative contributions from different geographical regions and source sectors depend on seasons and the locations in the HTP. The largest contribution to annual mean BC burden and surface deposition in the entire HTP region is from biofuel and biomass (BB) emissions in South Asia, followed by fossil fuel (FF) emissions from South Asia, then FF from East Asia. The same roles hold for all the seasonal means except for the summer when East Asia FF becomes more important. For finer receptor regions of interest, South Asia BB and FF have the largest impact on BC in Himalayas and Central Tibetan Plateau, while East Asia FF and BB contribute the most to Northeast Plateau in all seasons and Southeast Plateau in the summer. Central Asia and Middle East FF emissions have relatively more important contributions to BC reaching Northwest Plateau, especially in the summer. Although local emissions only contribute about 10% to BC in the HTP, this contribution is extremely sensitive to local emission changes. Lastly, we show that the annual mean radiative forcing (0.42 W m−2) due to BC in snow outweighs the BC dimming effect (−0.3 W m−2) at the surface over the HTP. We also find strong seasonal and spatial variation with a peak value of 5 W m−2 in the spring over Northwest Plateau. Such a large forcing of BC in snow is sufficient to cause earlier snow melting and potentially contribute to the acceleration of glacier retreat.

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Impact of topography on black carbon transport to the southern Tibetan Plateau during the pre-monsoon season and its climatic implication

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-5923-2020 ◽

2020 ◽

Vol 20 (10) ◽

pp. 5923-5943 ◽

Cited By ~ 2

Author(s):

Meixin Zhang ◽

Chun Zhao ◽

Zhiyuan Cong ◽

Qiuyan Du ◽

Mingyue Xu ◽

...

Keyword(s):

Tibetan Plateau ◽

Black Carbon ◽

Radiative Forcing ◽

Monsoon Season ◽

Radiative Heating ◽

The Tibetan Plateau ◽

Complex Topography ◽

Meridional Transport ◽

Near Surface ◽

Mass Volume

Abstract. Most previous modeling studies about black carbon (BC) transport and its impact over the Tibetan Plateau (TP) conducted simulations with horizontal resolutions coarser than 20 km that may not be able to resolve the complex topography of the Himalayas well. In this study, the two experiments covering all of the Himalayas with the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) at the horizontal resolution of 4 km but with two different topography datasets (4 km complex topography and 20 km smooth topography) are conducted for pre-monsoon season (April 2016) to investigate the impacts of topography on modeling the transport and distribution of BC over the TP. Both experiments show the evident accumulation of aerosols near the southern Himalayas during the pre-monsoon season, consistent with the satellite retrievals. The observed episode of high surface BC concentration at the station near Mt. Everest due to heavy biomass burning near the southern Himalayas is well captured by the simulations. The simulations indicate that the prevailing upflow across the Himalayas driven by the large-scale westerly and small-scale southerly circulations during the daytime is the dominant transport mechanism of southern Asian BC into the TP, and it is much stronger than that during the nighttime. The simulation with the 4 km topography resolves more valleys and mountain ridges and shows that the BC transport across the Himalayas can overcome the majority of mountain ridges, but the valley transport is more efficient. The complex topography results in stronger overall cross-Himalayan transport during the simulation period primarily due to the strengthened efficiency of near-surface meridional transport towards the TP, enhanced wind speed at some valleys and deeper valley channels associated with larger transported BC mass volume. This results in 50 % higher transport flux of BC across the Himalayas and 30 %–50 % stronger BC radiative heating in the atmosphere up to 10 km over the TP from the simulation with the 4 km complex topography than that with the 20 km smoother topography. The different topography also leads to different distributions of snow cover and BC forcing in snow. This study implies that the relatively smooth topography used by the models with resolutions coarser than 20 km may introduce significant negative biases in estimating light-absorbing aerosol radiative forcing over the TP during the pre-monsoon season. Highlights. The black carbon (BC) transport across the Himalayas can overcome the majority of mountain ridges, but the valley transport is much more efficient during the pre-monsoon season. The complex topography results in stronger overall cross-Himalayan transport during the study period primarily due to the strengthened efficiency of near-surface meridional transport towards the TP, enhanced wind speed at some valleys and deeper valley channels associated with larger transported BC mass volume. The complex topography generates 50 % higher transport flux of BC across the Himalayas and 30 %–50 % stronger BC radiative heating in the atmosphere up to 10 km over the Tibetan Plateau (TP) than the smoother topography, which implies that the smooth topography used by the models with relatively coarse resolution may introduce significant negative biases in estimating BC radiative forcing over the TP during the pre-monsoon season. The different topography also leads to different distributions of snow cover and BC forcing in snow over the TP.

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Source attribution of black carbon and its direct radiative forcing in China

10.5194/acp-2016-1032 ◽

2016 ◽

Author(s):

Yang Yang ◽

Hailong Wang ◽

Steven J. Smith ◽

Po-Lun Ma ◽

Philip J. Rasch

Keyword(s):

Air Quality ◽

East Asia ◽

Black Carbon ◽

Radiative Forcing ◽

North China ◽

Local Source ◽

Near Surface ◽

Direct Radiative Forcing ◽

Non Local ◽

Local Emissions

Abstract. The source attributions for mass concentration, haze formation, transport, and direct radiative forcing of black carbon (BC) in various regions of China are quantified in this study using the Community Earth System Model (CESM) with a source-tagging technique. Anthropogenic emissions are from the Community Emissions Data System that is newly developed for the Coupled Model Intercomparison Project Phase 6 (CMIP6). Over North China where the air quality is often poor, about 90 % of near-surface BC concentration is contributed by local emissions. 30 % of BC concentration over South China in winter can be attributed to emissions from North China and 10 % comes from sources outside China in spring. For other regions in China, BC is largely contributed from non-local sources. We further investigated potential factors that contribute to the poor air quality in China. During polluted days, a net inflow of BC transported from non-local source regions associated with anomalous winds plays an important role in increasing local BC concentrations. BC-containing particles emitted from East Asia can also be transported across the Pacific. Our model results show that emissions from inside and outside China are equally important for the BC outflow from East Asia, while emissions from China account for 7 % of BC concentration and 25 % in column burden in western United States in spring. Radiative forcing estimated shows that 66 % of the annual mean BC direct radiative forcing (2.3 W m−2) in China results from local emissions, and the remaining 34 % are contributed by emissions outside of China. Efficiency analysis shows that reduction in BC emissions over eastern China could benefit more on the regional air quality in China, especially in winter haze season.

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Source attribution of black carbon and its direct radiative forcing in China

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-4319-2017 ◽

2017 ◽

Vol 17 (6) ◽

pp. 4319-4336 ◽

Cited By ~ 36

Author(s):

Yang Yang ◽

Hailong Wang ◽

Steven J. Smith ◽

Po-Lun Ma ◽

Philip J. Rasch

Keyword(s):

Air Quality ◽

East Asia ◽

Black Carbon ◽

Radiative Forcing ◽

North China ◽

Eastern China ◽

Coupled Model ◽

Near Surface ◽

Direct Radiative Forcing ◽

Local Emissions

Abstract. The source attributions for mass concentration, haze formation, transport and direct radiative forcing of black carbon (BC) in various regions of China are quantified in this study using the Community Earth System Model (CESM) with a source-tagging technique. Anthropogenic emissions are from the Community Emissions Data System that is newly developed for the Coupled Model Intercomparison Project Phase 6 (CMIP6). Over north China where the air quality is often poor, about 90 % of near-surface BC concentration is contributed by local emissions. Overall, 35 % of BC concentration over south China in winter can be attributed to emissions from north China, and 19 % comes from sources outside China in spring. For other regions in China, BC is largely contributed from nonlocal sources. We further investigated potential factors that contribute to the poor air quality in China. During polluted days, a net inflow of BC transported from nonlocal source regions associated with anomalous winds plays an important role in increasing local BC concentrations. BC-containing particles emitted from East Asia can also be transported across the Pacific. Our model results show that emissions from inside and outside China are equally important for the BC outflow from East Asia, while emissions from China account for 8 % of BC concentration and 29 % in column burden in the western United States in spring. Radiative forcing estimates show that 65 % of the annual mean BC direct radiative forcing (2.2 W m−2) in China results from local emissions, and the remaining 35 % is contributed by emissions outside of China. Efficiency analysis shows that a reduction in BC emissions over eastern China could have a greater benefit for the regional air quality in China, especially in the winter haze season.

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Global source attribution of sulfate concentration, direct and indirect radiative forcing

10.5194/acp-2017-303 ◽

2017 ◽

Author(s):

Yang Yang ◽

Hailong Wang ◽

Steven J. Smith ◽

Richard Easter ◽

Po-Lun Ma ◽

...

Keyword(s):

Southeast Asia ◽

East Asia ◽

South Asia ◽

Central Asia ◽

Southern Hemisphere ◽

North Africa ◽

Radiative Forcing ◽

Sulfate Concentration ◽

Near Surface ◽

Indirect Radiative Forcing

Abstract. The global source-receptor relationships of sulfate concentration, direct and indirect radiative forcing (DRF and IRF) from sixteen regions/sectors for years 2010–2014 are examined in this study through utilizing a sulfur source-tagging capability implemented in the Community Earth System Model (CESM) with winds nudged to reanalysis data. Sulfate concentrations are mostly contributed by local emissions in regions with high emissions, while over regions with relatively low SO2 emissions, the near-surface sulfate concentrations are primarily attributed to non-local sources from long-range transport. The export of SO2 and sulfate from Europe contributes 16–20 % of near-surface sulfate concentrations over North Africa, Russia/Belarus/Ukraine (RBU) region and Central Asia. Sources from the Middle East account for 15–24 % of sulfate over North Africa, Southern Africa and Central Asia in winter and autumn, and 19 % over South Asia in spring. Sources in RBU account for 21–42 % of sulfate concentrations over Central Asia. East Asia accounts for about 50 % of sulfate over Southeast Asia in winter and autumn, 15 % over RBU in summer, and 11 % over North America in spring. South Asia contributes to 11–24 % of sulfate over Southeast Asia in winter and spring. Regional source efficiencies of sulfate concentrations are higher over regions with dry atmospheric conditions and less export, suggesting that lifetime of aerosols, together with regional export, is important in determining regional air quality. The simulated global total sulfate DRF is −0.42 W m−2, with 0.31 W m−2 contributed by anthropogenic sulfate and −0.11 W m−2 contributed by natural sulfate, relative to a state with no sulfur emissions. In the Southern Hemisphere tropics, dimethyl sulfide (DMS) contributes 17–84 % to the total DRF. East Asia has the largest contribution of 20–30 % over the Northern Hemisphere mid- and high-latitudes. A 20 % perturbation of sulfate and its precursor emissions gives a sulfate incremental IRF of −0.44 W m−2. DMS has the largest contribution, explaining −0.23 W m−2 of the global sulfate incremental IRF. Incremental IRF over regions in the Southern Hemisphere with low background aerosols is more sensitive to emission perturbation than those over the polluted Northern Hemisphere.

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Simulations of Black Carbon Over Indian Region: Improvements and Implications of Diurnality in Emissions

10.5194/acp-2019-152 ◽

2019 ◽

Author(s):

Gaurav Govardhan ◽

Sreedharan Krishnakumari Satheesh ◽

Krishnaswamy Krishna Moorthy ◽

Ravi Nanjundiah

Keyword(s):

Boundary Layer ◽

Black Carbon ◽

Radiative Forcing ◽

Regional Scale ◽

Early Morning ◽

Temporal Variations ◽

Indian Region ◽

Near Surface ◽

Aerosol Radiative Forcing ◽

Convective Mixing

Abstract. With a view to improving the performance of WRF-Chem over the Indian region in simulating BC (black Carbon) mass concentrations as well as its short-term variations, especially on diurnal scale, a region-specific diurnal variation scheme has been introduced in the model emissios and the performance of the modified simulations has been evaluated against high-resolution measurements carried out over 8 ARFI (Aerosol Radiative Forcing over India) network observatories spread across India for distinct seasons; pre-monsoon (represented by May), post-monsoon (represented by October) and winter (represented by December). In addition to an overall improvement in the simulated concentrations and their temporal variations, it has also been found that the effects of prescribing diurnally varying emissions on the simulated near-surface concentrations largely depend on the boundary layer turbulence. The effects are perceived fast (within about 2–3 hours) during the evening–early morning hours when the atmospheric boundary layer is shallow and convective mixing is weak, while they are delayed, taking as much as about 5–6 hours, during periods when the boundary layer is deep and convective mixing is strong. This information would also serve as an important input for agencies concerned with urban planning and pollution mitigation. Despite these improvements in the near-surface concentrations, the simulated columnar aerosol optical depth (AOD) still remains largely underestimated vis-a-vis the satellite retrieved products. These modifications will serve as a guideline for further model-improvement initiatives at regional scale.

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Simulations of black carbon over the Indian region: improvements and implications of diurnality in emissions

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-8229-2019 ◽

2019 ◽

Vol 19 (12) ◽

pp. 8229-8241 ◽

Cited By ~ 3

Author(s):

Gaurav Govardhan ◽

Sreedharan Krishnakumari Satheesh ◽

Krishnaswamy Krishna Moorthy ◽

Ravi Nanjundiah

Keyword(s):

Boundary Layer ◽

Black Carbon ◽

Radiative Forcing ◽

Regional Scale ◽

Early Morning ◽

Temporal Variations ◽

Indian Region ◽

Near Surface ◽

Aerosol Radiative Forcing ◽

Convective Mixing

Abstract. With a view to improving the performance of WRF-Chem over the Indian region in simulating BC (black carbon) mass concentrations as well as its short-term variations, especially on a diurnal scale, a region-specific diurnal variation scheme has been introduced in the model emissions and the performance of the modified simulations has been evaluated against high-resolution measurements carried out over eight ARFI (Aerosol Radiative Forcing over India) network observatories spread across India for distinct seasons: pre-monsoon (represented by May), post-monsoon (represented by October) and winter (represented by December). In addition to an overall improvement in the simulated concentrations and their temporal variations, we have also found that the effects of prescribing diurnally varying emissions on the simulated near-surface concentrations largely depend on the boundary layer turbulence. The effects are perceived quickly (within about 2–3 h) during the evening–early morning hours when the atmospheric boundary layer is shallow and convective mixing is weak, while they are delayed, taking as much as about 5–6 h, during periods when the boundary layer is deep and convective mixing is strong. This information would also serve as an important input for agencies concerned with urban planning and pollution mitigation. Despite these improvements in the near-surface concentrations, the simulated columnar aerosol optical depth (AOD) still remains largely underestimated vis-à-vis the satellite-retrieved products. These modifications will serve as a guideline for further model-improvement initiatives at a regional scale.

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Simulation of dust aerosol and its regional feedbacks over East Asia using a regional climate model

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-8-4625-2008 ◽

2008 ◽

Vol 8 (2) ◽

pp. 4625-4667 ◽

Cited By ~ 1

Author(s):

D. F. Zhang ◽

A. S. Zakey ◽

X. J. Gao ◽

F. Giorgi

Keyword(s):

East Asia ◽

Regional Climate Model ◽

Radiative Forcing ◽

Climate Model ◽

Regional Climate ◽

Surface Cooling ◽

Near Surface ◽

Dust Aerosols ◽

Source Regions ◽

Mass Load

Abstract. The ICTP regional climate model (RegCM3) coupled with a desert dust model is used to simulate the radiative forcing and related climate effects of dust aerosols over East Asia. Two sets of experiments encompassing the main dust producing months, February to May, for 10 years (1997–2006) are conducted and inter-compared, one without (Exp. 1) and one with (Exp. 2) the radiative effects of dust aerosols. The simulation results are evaluated against ground station and satellite data. The model captures the basic observed climatology over the area of interest. The spatial and temporal variations of near surface concentration, mass load, and emission of dust aerosols from the main source regions are reproduced by model, with the main model deficiency being an overestimate of dust amount over the source regions and underestimate downwind of these source areas. Both the top-of-the-atmosphere (TOA) and surface radiative fluxes are decreased by dust and this causes a surface cooling locally up to −1°C. The inclusion of dust radiative forcing leads to a reduction of dust emission in the East Asia source regions, which is mainly caused by an increase in local stability and a corresponding decrease in dust lifting. Our results indicate that dust effects should be included in the assessment of climate change over East Asia.

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Fire emission heights in the climate system – Part 2: Impact on transport, black carbon concentrations and radiation

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-7173-2015 ◽

2015 ◽

Vol 15 (13) ◽

pp. 7173-7193 ◽

Cited By ~ 18

Author(s):

A. Veira ◽

S. Kloster ◽

N. A. J. Schutgens ◽

J. W. Kaiser

Keyword(s):

Black Carbon ◽

Radiative Forcing ◽

General Circulation ◽

Circulation Model ◽

Atmospheric Radiation ◽

Orthogonal Polarization ◽

Plume Height ◽

Near Surface ◽

The Impact ◽

Emission Height

Abstract. Wildfires represent a major source for aerosols impacting atmospheric radiation, atmospheric chemistry and cloud micro-physical properties. Previous case studies indicated that the height of the aerosol–radiation interaction may crucially affect atmospheric radiation, but the sensitivity to emission heights has been examined with only a few models and is still uncertain. In this study we use the general circulation model ECHAM6 extended by the aerosol module HAM2 to investigate the impact of wildfire emission heights on atmospheric long-range transport, black carbon (BC) concentrations and atmospheric radiation. We simulate the wildfire aerosol release using either various versions of a semi-empirical plume height parametrization or prescribed standard emission heights in ECHAM6-HAM2. Extreme scenarios of near-surface or free-tropospheric-only injections provide lower and upper constraints on the emission height climate impact. We find relative changes in mean global atmospheric BC burden of up to 7.9±4.4 % caused by average changes in emission heights of 1.5–3.5 km. Regionally, changes in BC burden exceed 30–40 % in the major biomass burning regions. The model evaluation of aerosol optical thickness (AOT) against Moderate Resolution Imaging Spectroradiometer (MODIS), AErosol RObotic NETwork (AERONET) and Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) observations indicates that the implementation of a plume height parametrization slightly reduces the ECHAM6-HAM2 biases regionally, but on the global scale these improvements in model performance are small. For prescribed emission release at the surface, wildfire emissions entail a total sky top-of-atmosphere (TOA) radiative forcing (RF) of −0.16±0.06 W m−2. The application of a plume height parametrization which agrees reasonably well with observations introduces a slightly stronger negative TOA RF of −0.20±0.07 W m−2. The standard ECHAM6-HAM2 model in which 25 % of the wildfire emissions are injected into the free troposphere (FT) and 75 % into the planetary boundary layer (PBL), leads to a TOA RF of −0.24±0.06 W m−2. Overall, we conclude that simple plume height parametrizations provide sufficient representations of emission heights for global climate modeling. Significant improvements in aerosol wildfire modeling likely depend on better emission inventories and aerosol process modeling rather than on improved emission height parametrizations.

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