Beyond common urban air quality assessment: Relationship between PM2.5 and black carbon during haze and non-haze periods in Bangkok

Abstract

The atmospheric pollution burden in Bangkok, Thailand, is likely to be similar to that of other large urban agglomerations. Black carbon (BC) aerosol is one of the key components of PM2.5 (particulate matter with equivalent diameter ≤2.5 μm) pollutants; jointly they adversely affect humans and the environment. This study assessed the BC and PM2.5 ambient concentrations in Bangkok over nine months (November 1, 2020, to July 27, 2021), focusing on seasonal differences during the haze period (Hp; december 2020 to February 2021) and non-haze period (NHP; remaining months). PM2.5 data were measured optically, together with filter sampling of particles at heights of 30, 75, and 110 m above ground level (AGL). A thermal/optical carbon analysis method was used to determine the BC mass concentrations in the collected samples. The results showed that the vertically averaged BC concentration within PM2.5 increased more than 3-fold from 2.82 to 9.09 μg/m3 from the NHP to the HP. The vertical dependence of BC concentration was characterized by an increase in the height AGL in the NHP. In contrast, the opposite trend was observed for the HP. The average values of the PM2.5/BC ratio at all heights AGL showed a seasonal trend, with the BC mass concentration accounting for over 25% of PM2.5 concentration during the peak of the haze season.