Black carbon (BC) is a major pollutant entering the human body through PM2.5 and posing major health effects. India lying in the Asia region is a major contributor to BC emissions from the combustion of biofuels. BC present in the atmosphere is a pollutant deteriorating air quality and is a light-absorbing aerosol (LAA), thus playing a dual role. In India, several studies have been published quantifying BC concentration. The optical measurement of BC has been carried out at multiple locations in India, and its radiative effect has been studied using the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model. This review is an attempt to collate those studies that have measured BC and estimated its radiative effect. The BC levels, spectral Aerosol Optical Depth (AOD), single scattering albedo (SSA) and direct radiative forcing (DRF) at the top of the atmosphere (TOA), at the surface (SUR) and heat within the atmosphere (ATM) for 20 years (2002 to 2023) have been analysed. It was found that many studies for performing DRF calculations have not used BC measurements and have used AOD analysis to characterise the sources of aerosols as direct BC measurements are not required to estimate the DRF. The selection of AOD wavelength 500 nm or 550 nm is not clear in the literature for BC-RF calculations and needs to be standardised for DRF. IPCC AR6 has estimated Effective Radiative Forcing (ERF) due to BC with temperature and surface feedbacks, and future studies for ERF need to use climate models with tools like WRF-Chem. The source of BC is mostly from fossil fuel or biomass burning during the winter season, while it is dust aerosols during the summer. Biomass burning, use of traditional cook stoves and aerosol episodes contribute to the warming of the ambient environment. Beijing, China, has reduced ATM forcing in the summer when compared to Delhi, India, and has reduced the fraction of heat exerted in the atmosphere. The interactions of BC-UHI are not studied yet in India, and with the ARFINET network, an attempt can be made in this direction. The Urban Pollution Island (UPI)-Urban Heat Island (UHI) review identified PM2.5 contributing to UHI intensity during the summer and winter in metro cities, while BC-UHI interactions are not dealt with in detail.

The regional climate model RegCM 4.4 at 50km resolution is used to conduct a sensitivity study over South Asia Coordinated Regional climate Downscaling Experiment domain during the period 1998-2002, in order to investigate the best cumulus convective precipitation scheme, planetary boundary layer (PBL) and land-surface scheme. The inferences obtained from 11 sensitivity experiments include the better performance of community land model version 4.5 (CLM 4.5) over biosphere-atmosphere transfer scheme, Tiedtke as cumulus convective precipitation scheme and University of Washington (UW) as PBL scheme. The simulation with these parameterization schemes well captures the monsoon precipitation pattern over India similar to 7mm/day and North Eastern Region of India (NER) similar to 12mm/day, which are comparable to observations with a significant correlation of R-2>0.93. The observed temperatures are also well simulated by the model. Therefore, RegCM 4.4 with these parameterization schemes is further used to simulate the aerosol fields (aerosol optical depth, AOD and black carbon, BC) and aerosol direct radiative forcing (DRF) for the period 2011-2014 over the same domain with special emphasis on NER. The model captures the seasonality in AOD and BC over the Indian Subcontinent and NER. BC hotspots in the Indo-Gangetic Plain and China are well captured by the model. The observed to simulated BC ratio over Dibrugarh (located in NER) is found to be improved. The model underestimation is significant in the dry season when burning over the region is predominant, which has not been considered by the emission inventories properly. Simulated DRF is found to exhibit seasonality qualitatively as well as a North-South latitudinal gradient.

This study applies the nested-grid version of Goddard Earth Observing System (GEOS) chemical transport model (GEOS-Chem) to examine future changes (2000-2050) in SOA concentration and associated direct radiative forcing (DRF) over China under the Representative Concentration Pathways (RCPs). The projected changes in SOA concentrations over 2010-2050 generally follow future changes in emissions of toluene and xylene. On an annual mean basis, the largest increase in SOA over eastern China is simulated to be 25.1% in 2020 under RCP2.6, 20.4% in 2020 under RCP4.5, 56.3% in 2050 under RCP6.0, and 44.6% in 2030 under RCP8.5. The role of SOA in PM2.5 increases with each decade in 2010-2050 under RCP2.6, RCP4.5, and RCPS.5, with a maximum ratio of concentration of SOA to that of PM2.5 of 16.3% in 2050 under RCP4.5 as averaged over eastern China (20 degrees-45 degrees N, 100 degrees-125 degrees E). Concentrations of SOA are projected to be able to exceed those of sulfate, ammonium, and black carbon (BC) in the future. The future changes in SOA levels over eastern China are simulated to lead to domain-averaged (20 degrees-45 degrees N, 100 degrees-125 degrees E) DRI's of +0.19 W m(-2), +0.12 W m(-2), -0.28 W m(-2), and -0.17 W m(-2) in 2050 relative to 2000 under RCP2.6, RCP4.5, RCP6.0, and RCP8.5, respectively. Model results indicate that future changes in SOA owing to future changes in anthropogenic precursor emissions are important for future air quality planning and climate mitigation measures. (C) 2018 Elsevier B.V. All rights reserved.