This study reports black carbon (BC) characteristics and climate effects for a 22-month period during 2018-2020 at a receptor location in the eastern Indo-Gangetic Plains (IGP). The overall averaged BC mass concentration was 7.8 & PLUSMN; 4.7 & mu;g m- 3, and the nighttime average (9.1 & PLUSMN; 6.1 & mu;g m- 3) was nearly double that of the daytime (5.8 & PLUSMN; 3.5 & mu;g m- 3). BC was most enhanced during winter, with mean concentration (14.3 & PLUSMN; 3.8 & mu;g m- 3) higher by 4 times as compared to summer. A two-component mixing model, frequency distribution of the Angstrom exponent, and a simultaneous increase in brown carbon (BrC) absorption coefficient suggested that this enhancement was mostly due to the biomass burning (BB) fraction of BC. CALIPSO-derived products showed that the extinction coefficient was highest at 0.62 & PLUSMN; 0.31 km-1 in winter and lowest at 0.12 & PLUSMN; 0.05 km-1 in summer. Backscatter plots and particle depolarization ratios indicated presence of spherical dust particles during summer and smoke plumes during post-monsoon and winter. Concentration-weighted trajectories (CWTs) helped in quantifying significant contributions of the IGP outflow to BC, BC-BB and BrC absorption. Finally, a large direct radiative forcing of the atmosphere by BC (37 & PLUSMN; 22 W m- 2) was estimated via the radiative transfer model SBDART, with an associated atmospheric heating rate of 1.02 K d-1.

The study examines the thermodynamic structure of the marine atmospheric boundary layer (MABL) and its effect on the aerosol dynamics in the Indian Ocean sector of Southern Ocean (ISSO) between 30 degrees S-67 degrees S and 57 degrees E-77 degrees E. It includes observations of aerosols and meteorology collected during the Xth Southern Ocean Expedition conducted in December 2017. The results revealed the effect of frontal-region-specific air-sea coupling on the thermodynamic structure of MABL and its role in regulating aerosols in ISSO. The MABL over the subtropical front was unstable and formed a well-evolved mixed layer ( 2400 m) capped by low-level inversions ( 660 m). Convective activities in the Sub-Antarctic Frontal region were associated with the Agulhas Retroflection Current, which supported the forma-tion of a well-developed mixed layer ( 1860 m). The mean estimates of aerosol optical depth (AOD) and black carbon (BC) mass concentrations were 0.095 +/- 0.006 and 50 +/- 14 ng m-3, respectively, and the resultant clear sky direct shortwave radiative forcing (DARF) and atmospheric heating rate (HR) were 1.32 +/- 0.11 W m-2 and 0.022 +/- 0.002 K day-1, respectively. In the polar front (PF) region, frequent mid-latitude cyclones led to highly stabilized MABL, supported low-level multi-layered clouds (>3-layers) and multiple high-level inversions (strength > 0.5 K m-1 > 3000 m). The clouds were mixed-phased with temperatures less than -12 degrees C at 3000 m altitude. Interestingly, there was higher loading of dust and BC aerosols (276 +/- 24 ng m-3), maximum AOD (0.109 +/- 0.009), clear sky DARF (1.73 +/- 0.02 W m-2), and HR (0.029 +/- 0.005 K day-1). This showed an accumulation of long-range advected anthro-pogenic aerosols within baroclinic-boundaries formed over the PF region. Specifically, in the region south of PF, weak convection caused weakly-unstable MABL with a single low-level inversion followed by no clouds/single-layer clouds. Predominant clean maritime air holding a small fraction of dust and BC accounted for lower estimates of AOD (0.071 +/- 0.004), BC concentrations (90 +/- 55 ng m-3) and associated clear sky DARF and HR were 1.16 +/- 0.06 W m-2 and 0.019 +/- 0.001 K day-1, respectively.

The optical and radiative characteristics of water-soluble and carbonaceous aerosol species in the PM2.5 samples were examined for a representative megacity over the Indo-Gangetic Basin (IGB). Aerosol optical and radiative transfer models were used to extract sulphate (SO4), nitrate (NO3), organic carbon (OC) and elemental carbon (EC) from the observations done in 2012. Initial results suggest that the mass concentration of OC dominated over other species, but impacts on optical characteristics were mostly due to the SO4 aerosols. Further, EC shows relatively large impact on radiative forcing. The aerosol optical depth (AOD) at 500 nm for SO4, NO3, EC and OC was found to be contributing similar to 36%, 20%, 27% and 9%, respectively in the total AOD value (0.61 +/- 0.18) during the entire study period. The single scattering albedo (SSA) for SO4 and NO3 was high and suggested their scattering nature; however, being the highly absorbing species, EC was found to show the lowest values of SSA during the study period. SSA for OC was, however, similar to 0.70, which was found to show the second highest warming species in the atmosphere with contribution of similar to 10%, after EC, which caused the highest warming (similar to 70%), to the total atmospheric forcing.

The simultaneous near surface measurements of aerosol scattering and absorption coefficients over different environments (Ahmedabad, urban and Gurushikhar, a high altitude remote site) in western India were conducted to estimate SSA and investigate the importance of SSA in aerosol radiative forcing. The surface SSA (0.79, 0.85) is lower than the column SSA (0.92, 0.95) as emission sources for black carbon aerosols (absorbing in nature) are abundant near the surface (Ahmedabad, Gurushikhar). The atmospheric warming over the urban region estimated using column SSA is a factor of 3 lower ( similar to 18 Wm(-2)) than that of the warming ( similar to 52 Wm(-2)) estimated utilising surface SSA. The significant difference in atmospheric warming arises due to the differences in the SSA as aerosol optical depth (a measure of column concentration of aerosols) is the same. Surface and column SSA are comparatively higher over the high altitude remote site as the abundance of absorbing aerosols is less over a non-source region. In addition, the differences between surface and column SSA are less (< 9%) resulting in comparable aerosol radiative forcing estimates. This study highlights the differences that can arise in aerosol radiative effects due to the differences in SSA as a function of altitude (surface vs. column) and environment (urban vs. remote), thereby providing regional bounds on aerosol radiative forcing which can further be used in climate assessment studies.

Observations on black carbon (BC) aerosols over an urban site (Pune) and a rural, high altitude site (Sinhagad) during summer and winter seasons over the period of 2009-2013 are reported. Apart from the temporal variation of BC over both the sites, its mass fraction to total suspended particulates (TSP) is studied. Finally, using the chemical composition of TSP and BC in the OPAC model, season-wise optical properties of aerosols are obtained which are further used in the SBDART model to derive the aerosol radiative forcing (ARF) at surface and top of the atmosphere and thereby the atmospheric forcing and heating rates in each season over both the sites. BC mass concentration and its mass fraction to TSP (Mf BC) were higher at Pune than at Sinhagad, indicating impact of more anthropogenic sources. At both the sites winter season witnessed higher BC concentrations than summer as well as higher Mf BC which is due to the prevailing favorable meteorological conditions in winter. Diurnal variation of BC showed different patterns at Pune and Sinhagad in terms of strength and occurrence of high and low values that could be attributed to varying local boundary layer conditions and source activities at both the sites. Negative ARF indicated cooling at top of the atmosphere and at surface leading to warming of the atmosphere at both the sites. However, surface cooling and atmospheric warming was more dominant at Pune leading to higher atmospheric heating rates, underlining the impact of absorbing BC aerosols which were about three times more at Pune than Sinhagad. (C) 2015 Elsevier Ltd. All rights reserved.

The higher altitude regions of Himalayas and Tibetan Plateau are influenced by the dust and black carbon (BC) aerosols from the emissions and long-range transport from the adjoining areas. In this study, we present impacts of advection of polluted air masses of natural and anthropogenic emissions, on aerosol optical and radiative properties at Manora Peak (similar to 2000 m amsl) in central Himalaya over a period of more than two years (February 2006-May 2008). We used the most updated and comprehensive data of chemical and optical properties available in one of the most climatically sensitive region, the Himalaya, to estimate atmospheric radiative forcing and heating rate. Aerosol optical depth (ADD) was found to vary from 0.04 to 0.45 with significantly higher values in summer mainly due to an increase in mineral dust and biomass burning aerosols due to transport. In contrast, single scattering albedo (SSA) varied from 0.74 to 0.88 with relatively lower values during summer, suggesting an increase in absorbing BC and mineral dust aerosols. As a result, a large positive atmospheric radiative forcing (about 28 5 Wm(-2)) and high values of corresponding heating rate (0.80 +/- 0.14 Kday(-1)) has been found during summer. During the entire observation period, radiative forcing at the top of the atmosphere varied from 2 to +14 Wm(-2) and from -3 to -50 Wm(-2) at the surface whereas atmospheric forcing was in the range of 3 to 65 Wm(-2) resulting in a heating rate of 0.1-1.8 Kday(-1). (C) 2014 Elsevier B.V. All rights reserved.

The present work is aimed to understand direct radiation effects due to aerosols over Delhi in the Indo-Gangetic Basin (IGB) region, using detailed chemical analysis of surface measured aerosols during the year 2007. An optically equivalent aerosol model was formulated on the basis of measured aerosol chemical compositions along with the ambient meteorological parameters to derive radiatively important aerosol optical parameters. The derived aerosol parameters were then used to estimate the aerosol direct radiative forcing at the top of the atmosphere, surface, and in the atmosphere. The anthropogenic components measured at Delhi were found to be contributing similar to 72% to the composite aerosol optical depth (AOD(0.5) similar to 0.84). The estimated mean surface and atmospheric forcing for composite aerosols over Delhi were found to be about -69, -85, and -78 W m(-2) and about +78, +98, and +79 W m(-2) during the winter, summer, and post-monsoon periods, respectively. The anthropogenic aerosols contribute similar to 90%, 53%, and 84% to the total aerosol surface forcing and similar to 93%, 54%, and 88% to the total aerosol atmospheric forcing during the above respective periods. The mean (+/- SD) surface and atmospheric forcing for composite aerosols was about -79 (+/- 15) and +87 (+/- 26) W m(-2) over Delhi with respective anthropogenic contributions of similar to 71% and 75% during the overall period of observation. Aerosol induced large surface cooling, which was relatively higher during summer as compared to the winter suggesting an increase in dust loading over the station. The total atmospheric heating rate at Delhi averaged during the observation was found to be 2.42 +/- 0.72 K day(-1), of which the anthropogenic fraction contributed as much as similar to 73%.