Temporal Characteristics of Brown Carbon over the Central Indo-Gangetic Plain

Recent global models estimate that light absorption by brown carbon (BrC) in several regions of the world is similar to 30-70% of that due to black carbon (BC). It is, therefore, important to understand its sources and characteristics on temporal and spatial scales. In this study, we conducted semicontinuous measurements of water-soluble organic carbon (WSOC) and BrC using particle-into:liquid sampler coupled with a liquid waveguide capillary cell and total organic carbon analyzer (PILS-LWCC-TOC) over Kanpur (26.5 degrees N, 80.3 degrees E, 142 m amsl) during a winter season (December 2015 to February 2016). In addition, mass concentrations of organic and inorganic aerosol and BC were also measured. Diurnal variability in the absorption coefficient of BrC at 365 nm (b(abs)_(365)) showed higher values (35 +/- 21 Mm(-1)) during, late evening to early morning hours and was attributed to primary emissions from biomass burning (BB) and fossil fuel burning (FFB). The b(abs)_(365) reduced by more than 80% as the day progressed, which, was ascribed to photo bleaching/volatilization of BrC and/or due to rising boundary layer height. Further, diurnal variability in the ratios of b(abs)_(405)/b(abs_365) and,b(abs_420)/b(abs_365) suggests that the BrC composition was not uniform throughout a day. WSOC exhibited a strong correlation with 45365 (slope = 1.22 0.007, r(2) = 0.70,.n = 13 265, intercept =-0:69 +/- 0.17), suggesting the presence of a significant but variable fraction of chromopheres: Mass absorption efficiency (MAE) values of WSOC ranged from 0.003 to 5.26 m(2) g(-1) (1.16 +/- 0.60) during the study period. Moderate correlation (r(2) = 0.50, slope = 1.58 +/- 0.019, n = 6471) of babs 365 was observed with the seinivolatile oxygenated organic aerosols (SV-OOA) fraction of BB resolved from positive matrix factorization (PMF) analysis of organic mass spectral data Obtained from a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). The low-volatility 00A (LV-OOA) fraction of BB had a similar correlation to b(abs_365) (r(2) = 0.54, slope = 0.38 +/- 0.004, n = 6471) but appears to have a smaller contribution to the absorption!