Brown carbon in atmospheric outflow from the Indo-Gangetic Plain: Mass absorption efficiency and temporal variability

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.