The present study examines the aerosol characteristics over Patiala in northwestern India from October 2013 to June 2014. The average mass concentration of the total suspended particulates (TSP) varied from 117 to 301 mu g m(3), with PM10 accounting for similar to 63-83% from October to February (P1) and decreasing to less than similar to 40% from March to June (P2). The aerosol optical depth (AOD(500)) exhibited its highest values during October (0.818) and its lowest during April (0.332), with the wavelength dependence differing significantly on a temporal scale. The Angstrom exponent (alpha(380-870)) values indicated a relatively high quantity of fine-mode particles over the study region during P1 as compared to P2, which is consistent with the PM measurements. The average monthly mass concentration of the climate forcing agent black carbon (BC) varied from 2.4 to 12 mu g m(3), with the highest mass concentration in December and the lowest in June. The average monthly single scattering albedo (SSA(500)) derived from the OPAC (Optical Properties of Aerosols and Clouds) model varied from 0.890 to 0.947, with lower values during P1 than P2. The average monthly clear-sky direct atmospheric aerosol radiative forcing (ATM ARF) estimated by the SBDART (Santa Barbara DISORT Atmospheric Radiative Transfer) model ranged between +12 and +36 Wm(-2) over the study region. Even though the mass fraction of BC averaged over the study period was only 2.4% of the total mass of the composite aerosol, its contribution to net ATM ARF was found to be significant (> 60%), indicating that BC contributes significantly to warming on a regional scale. These results improve our understanding of the impact of BC and composite aerosol on the earth's radiation budget and hence on regional climate.

The simultaneous measurements of brown carbon (BrC) and elemental carbon (EC) are made in ambient aerosols (PM2.5), collected from a site in north-east India during November'09-March'10, representing the atmospheric outflow from the Indo-Gangetic Plain (IGP) to the Bay of Bengal (BoB). The absorption coefficient of BrC (b(abs)), assessed from water-soluble organic carbon (WSOC) at 365 nm, varies from 2 to 21 M m(-1) and exhibits significant linear relationship (P < 0.05) with WSOC concentration (3-29 mu g m(-3)). The angstrom exponent (alpha: 8.3 +/- 2.6, where b(abs) approximate to lambda(-alpha)) is consistent with that reported for humic-like substances (HULIS) from biomass burning emissions (BBE). The impact of BBE is also discernible from mass ratios of nss-K+/EC (0.2-1.4) and OC/EC (3.4-11.5). The mass fraction of WSOC (10-23%) in PM2.5 and mass absorption efficiency of BrC (sigma(abs-BrC): 0.5-1.2 m(2) g(-1)) bring to focus the significance of brown carbon in atmospheric radiative forcing due to anthropogenic aerosols over the Indo-Gangetic Plain. (C) 2014 Elsevier Ltd. All rights reserved.

The first field measurements of light absorbing water-soluble organic carbon (WSOC), referred as brown carbon (BrC), have been made in the marine atmospheric boundary layer (MABL) during the continental outflow to the Bay of Bengal (BoB) and the Arabian Sea (ARS). The absorption signal measured at 365 nm in aqueous extracts of aerosols shows a systematic linear increase with WSOC concentration, suggesting a significant contribution from BrC to the absorption properties of organic aerosols. The mass absorption coefficient (b(abs)) of BrC shows an inverse hyperbolic relation with wavelength (from 300 to 700 nm), providing an estimate of the Angstrom exponent (alpha P, range: 3-19; Av: 9 +/- 3). The mass absorption efficiency of brown carbon (sigma(abs) BrC) in the MABL varies from 0.17 to 0.72 m(2) g(-1) (Av: 0.45 +/- 0.14 m(2) g(-1)). The alpha P and sigma(abs) BrC over the BoB are quite similar to that studied from a sampling site in the Indo-Gangetic Plain (IGP), suggesting the dominant impact of organic aerosols associated with the continental outflow. A comparison of the mass absorption efficiency of BrC and elemental carbon (EC) brings to focus the significant role of light absorbing organic aerosols (from biomass burning emissions) in atmospheric radiative forcing over oceanic regions located downwind of the pollution sources.