Vertical variation of carbonaceous aerosols within the PM2.5 fraction in Bangkok, Thailand

Abstract

Asian megacities are undergoing rapid population and infrastructure growth, which is resulting in significant air quality problems linked to atmospheric fine particles (PM2.5). This study focuses on characterizing carbonaceous aerosols in an urban area of Bangkok, Thailand. The Microclimate and Air Pollutants Monitoring tower is located on the edge of Kasetsart University campus and was used to perform vertical measurements. Mass concentration data were collected using area dust monitors (ADR1500) at different levels above the ground (30 m, 75 m, and 110 m) during two time periods, daytime (08:00– 19:00) and nighttime (20:00–07:00), throughout the monsoon season in 2015. All relevant micrometeorological parameters were simultaneously monitored. Backward air mass trajectories were calculated using HYSPLIT to assess the possible external pollution contributions. The thermal optical transmittance (TOT) method following the NIOSH 870 protocol was used to determine amounts of elemental carbon (EC) and organic carbon (OC) in samples. A data analysis showed average PM2.5 values at observation heights of 30 m, 75 m, and 110 m of 6.21 ± 2.45, 8.12 ± 3.65, and 9.03 ± 3.93 µg m–3, respectively; corresponding OC concentrations of 4.13 ± 2.65, 4.01 ± 4.07, and 4.11 ± 3.58 µg m–3, respectively, and EC concentrations of 1.02 ± 0.84, 1.07 ± 0.95, and 0.50 ± 0.70 µg m–3, respectively. The results show distinct gradients of increasing concentrations of PM2.5 with increasing elevation in contract with the OC and EC concentrations which decrease with height.