PM2.5 Brown Carbon in Water and Methanol Extracts: Measurement and Estimation of Contributions to Fine Particle Light Absorption over Bhopal, Central India
ANKUR BHARDWAJ, Ramya Sunder Raman, Manju Galodiya,
Indian Institute of Science Education and Research Bhopal Abstract Number: 228
Working Group: Carbonaceous Aerosol
AbstractThe light-absorbing properties of water-soluble brown carbon (WS-BrC) and methanol-soluble brown carbon (MeS-BrC) were studied in ambient fine particulate (PM
2.5) aerosols collected at Bhopal, a regionally representative location in Central India during 2019 and 2020. Particulate organic carbon (OC), elemental carbon (EC), and WSOC were measured by thermal-optical carbon analysis and Total OC analysis method, respectively (349 quartz filter samples; 24-hour time-integrated). Particulate light-absorption was measured with a multi-wavelength thermal-optical carbon analyzer (DRI 2015; 405 - 980 nm), and solution light-absorption spectra of water and the methanol extracts were measured by UV-visible spectrophotometer (Agilent Cary 100/300; 300 - 800 nm). The light absorption coefficients (babs) of WS-BrC and MeS-BrC were highest during the post-monsoon and lowest during the monsoon seasons. MeS-BrC absorbs about 5 times higher at 365 nm and about 4 times more at 550 nm, compared to WS-BrC at these wavelengths. At 405 nm, light absorption by solution BrC on average were 6 ± 5 % (WS-BrC) and 10 ± 4 % (MeS-BrC) of particulate BrC absorption, while they were 4 ± 3 % (MeS-BrC) and 5 ± 2 % (WS-BrC) of particulate EC absorption. The mass absorption cross-section (MAC) of WS-BrC (1.9 ± 1.2 m
2 g
-1) and MeS-BrC (2.1 ± 1.1 m
2 g
-1) measured at 365 nm were similar to those observed previously at South and East Asian cities (Delhi, India and Xianghe, China). BrC concentrations in solution show that it is optically important in the near-UV range even during the monsoon season, when no biomass burning emissions occur (WS-BrC
405: ~3 ± 0.4 %; MeS-BrC
405: ~9 ± 4 % of total PM
2.5 light absorption).