PM2.5 carbonaceous components and mineral dust at a COALESCE network site - Bhopal, India: Estimating site-specific optical characteristics

Abstract

Atmospheric PM2.5 thermal elemental carbon (EC), optical black carbon (BC), brown carbon (BrC), and mineral dust (MD) were characterized during a field campaign at a regionally representative site (Bhopal, central India) all year-long during 2019. In this study, the optical characteristics of PM2.5 during ‘EC-rich’, ‘OC-rich’, and ‘MD-rich’ days were used in a three-component model to estimate site-specific Absorption Ångström exponent (AAE) and absorption coefficient (babs) of light-absorbing PM2.5 constituents. The AAE for ‘EC-rich’, ‘OC-rich’, and ‘MD-rich’ days were 1.1 ± 0.2, 2.7 ± 0.3, and 3.0 ± 0.9, respectively. The percentage contribution of calculated babs of EC, BrC, and MD to the total babs at 405 nm was dominated by EC during the entire study period (EC; 64 % ± 36 %, BrC: 30 % ± 5 %, MD: 10 % ± 1 %). Further, site-specific mass absorption cross-section (MAC) values were calculated to assess the impact of their use over the use of manufacturer-specified MAC values in estimating BC concentrations. The r2 between thermal EC and optical BC was higher (r2 = 0.67, slope = 1.1) when daily site-specific MAC values were used rather than using the default MAC value (16.6 m2 g−1; r2 = 0.54 and slope = 0.6). Overall, had the default MAC880 been used instead of the site-specific values, we would have underestimated the BC concentration by 39 % ± 18 % during the study period.