Characterization of PM_0.1 mass concentrations and elemental and organic carbon in upper Southeast Asia

Addressing the air pollution problem in upper Southeast Asia (USEA) becomes critical due to its serious impacts on human health and the environment. This study aims to investigate the characteristics of ultrafine carbonaceous particles (PM_0.1; Dp <≤ 0.1 μm) in Chiang Mai, Thailand, and Tachileik, Myanmar. Carbon compositions, including elemental carbon (EC) and organic carbon (OC) in PM_0.1, were determined by a carbon analyzer. The range of particle mass ranged from 3.2 to 18.4 μg/m³ with an average of 8.3 ± 4.4 μg/m³ and 5.4–20.8 μg/m³ with an average of 10.2 ± 4.3 μg/m³ in Thailand and Myanmar, respectively. The ratio of the EC, Char-EC/Soot-EC ratio, was found to be more applicable than the OC/EC ratio for identifying the sources of the emission. The char-EC/Soot-EC ratios in the PM_0.1 were less than 1.0 in the rainy season. Vehicle exhaust had a significant impact on these samples. However, the higher Char-EC/Soot-EC ratios indicate that biomass burning was a major source. The correlation for PM_0.1 with all carbon profiles was strong, especially during the dry season, suggesting that they were produced from the same emission source. The OC/EC vs. EC correlation for PM_0.1 at the Chiang Mai and Tachileik sites appears to be affected by open biomass fires. Our findings suggest that biomass combustion is a probable source of PM_0.1 in Thailand and Myanmar. Therefore, it is crucial to prioritize the management of open burning and traffic to mitigate PM_0.1 pollution in this region.