There is significant uncertainty in the global inventory of black carbon (BC). Several recent studies have reported BC emission updates, including the Fire Emission Inventory-northern Eurasia, anthropogenic emission in Russia, and global natural gas flaring. Compared with the inventory used by Intergovernmental Panel on Climate Change, these updates are only 10% higher on a global scale but are 3 times greater than previous estimations in Arctic (60-90 degrees N). We applied GEOS-Chem to examine these emission updates and evaluate their impacts on direct forcing. We found that Fire Emission Inventory-northern Eurasia may be substantially overestimated, Russia shows no prominent influence on simulation, and natural gas flaring noticeably improves simulation performance in the Arctic. Model estimated direct forcing of BC is increased by 30% on the global scale and is 2 times higher in the Arctic through application of these emission updates. This study reveals the urgent need to improve the reliability of emission inventories in the high latitudes, especially over Eurasia. Plain Language Summary Recent black carbon (BC) emission updates suggest a substantially higher inventory than that used by Intergovernmental Panel on Climate Change. Through GEOS-Chem modeling, we found that the Fire Emission Inventory-northern Eurasia biomass burning emission is overestimated over northern Eurasia, likely due to employment of U.S. plants species-based emission factors. Russian anthropogenic and natural gas flaring inventories help improve simulation performance in the Arctic. Model estimated direct forcing of BC is doubled when applying these emission updates, indicating the urgent need to further validate and improve the BC emission inventory.

The aerosol-cloud interactions due to black carbon (BC) aerosols, as well as the implied climate responses, are examined using an aerosol module in the coupled atmosphere-ocean general circulation model MPI-ESM. BC is simulated to enhance cloud droplet number concentration (CDNC) by 10-15% in the BC emission source regions, especially in the Tropics and mid-latitudes. Higher CDNC and reduced auto-conversion from cloud water to rain water explains the increased cloud water path over the tropical regions (30 degrees S-30 degrees N) in the model. In the global mean, the cloud water-as well as precipitation changes are negligibly small. The global-mean effective radiative forcing due to aerosol-cloud interactions for BC is estimated at -0.13 +/- 0.1 Wm(-2), which is attributable to the increase in CDNC burden and (regionally) cloud water in the model. Global mean temperature and rainfall response were found to be -0.16 +/- 0.04 K and -0.004 +/- 0.004 mm day(-1), respectively, with significantly larger regional changes mainly in the downwind regions from BC sources.

Black carbon (BC) induced indirect radiative forcing and cloud albedo effect has been studied for the first time over northeast India. Measurements of BC and cloud microphysical parameters were carried out during Phase-I of the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) over northeast India (Guwahati) in 2009. Liquid water path (LWP) in the cloud layers coherent with BC on different experimental days was found to be 206-327 g m(-2) over the region. Black carbon aerosol indirect effect (BCIE) for fixed LWP is found to be 0.32-0.48 on different days of observations. The indirect forcing corresponding to this BCIE has been estimated using a radiative transfer model for fixed LWP by altering the derived BC-AOD (aerosol optical depth from measured BC profiles) and cloud effective radius (R-e) combinations. The estimated average BC-induced indirect forcing (BCIF) was -24 to -37.1 W m(-2) at the surface and +2.5 to +14.8 W m(-2) at the top of the atmosphere (TOA). The average albedo due to BCIF at TOA was 0.49-0.61. BCIF is found to reduce the cloud reflection by 1.5-2% over the region. The sensitivities of cloud parameters to BCIF and the albedo effect are illustrated.

To assess individual direct radiative effects of diverse aerosol species on a regional scale, the air quality modeling system RAMS-CMAQ (Regional Atmospheric Modeling System and Community Multiscale Air Quality) coupled with an aerosol optical properties/radiative transfer module was used to simulate the temporal and spatial distributions of their optical and radiative properties over East Asia throughout 2005. Annual and seasonal averaged aerosol direct radiative forcing (ADRF) of all important aerosols and individual components, such as sulfate, nitrate, ammonium, black carbon (BC), organic carbon (OC), and dust at top-of-atmosphere (TOA) in clear sky are analyzed. Analysis of the model results shows that the annual average ADRF of all important aerosols was in the range of 0 to -18 W m(-2), with the maximum values mainly distributed over the Sichuan Basin. The direct radiative effects of sulfate, nitrate, and ammonium make up most of the total ADRF in East Asia, being concentrated mainly over North and Southeast China. The model domain is also divided into seven regions based on different administrative regions or countries to investigate detailed information about regional ADRF variations over East Asia. The model results show that the ADRFs of sulfate, ammonium, BC, and OC were stronger in summer and weaker in winter over most regions of East Asia, except over Southeast Asia. The seasonal variation in the ADRF of nitrate exhibited the opposite trend. A strong ADRF of dust mainly appeared in spring over Northwest China and Mongolia.

The air quality modeling system RAMS (Regional Atmospheric Modeling System)-CMAQ (Models-3 Community Multi-scale Air Quality) is developed to simulate the aerosol optical depth (AOD) and aerosol direct forcing (DF). The aerosol-specific extinction, single scattering albedo, and asymmetry factor are parameterized based on Mie theory taking into account the aerosol size distribution, composition, refractive index, and water uptake of solution particles. A two-stream solar radiative model considers all gaseous molecular absorption, Rayleigh scattering, and aerosols and clouds. RAMS-CMAQ is applied to simulate all major aerosol concentrations (e.g., sulfate, nitrate, ammonium, organic carbon, black carbon, fine soil, and sea salt) and AOD and DF over East Asia in 2005. To evaluate its performance, the simulated AOD values were compared with ground-based in situ measurements. The comparison shows that RAMS-CMAQ performed well in most of the model domain and generally captured the observed variations. High AOD values (0.2-1.0) mainly appear in the Sichuan Basin as well as in central and southeastern China The geographic distribution of DF generally follows the AOD distribution patterns, and the DF at the top-of-the-atmosphere is less than -25 and -20 W m(-2) in clear-sky and all-sky over the Sichuan Basin. Both AOD and DF exhibit seasonal variations with lower values in July and higher ones in January. The DF could obviously be impacted by high cloud fractions.