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

Rangu Satish, Puthukkadan Shamjad, Navaneeth Thamban, Sachchida Tripathi, Neeraj Rastogi*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

109 Citations (Scopus)

Abstract

Recent global models estimate that light absorption by brown carbon (BrC) in several regions of the world is ∼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°N, 80.3°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 (babs-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 babs-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 babs-405/babs-365 and babs-420/babs-365 suggests that the BrC composition was not uniform throughout a day. WSOC exhibited a strong correlation with babs-365 (slope = 1.22 ± 0.007, r2 = 0.70, n = 13 265, intercept = -0.69 ± 0.17), suggesting the presence of a significant but variable fraction of chromophores. Mass absorption efficiency (MAE) values of WSOC ranged from 0.003 to 5.26 m2 g-1 (1.16 ± 0.60) during the study period. Moderate correlation (r2 = 0.50, slope = 1.58 ± 0.019, n = 6471) of babs-365 was observed with the semivolatile 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 OOA (LV-OOA) fraction of BB had a similar correlation to babs-365 (r2 = 0.54, slope = 0.38 ± 0.004, n = 6471) but appears to have a smaller contribution to the absorption.

Original languageEnglish
Pages (from-to)6765-6772
Number of pages8
JournalEnvironmental Science and Technology
Volume51
Issue number12
DOIs
Publication statusPublished - 20 Jun 2017
Externally publishedYes

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