An Investigation of Carbonaceous Components and Source Identification of Ultrafine Particulate Matter in the Atmosphere of the Southern Region of Thailand

Abstract This study investigates the composition of carbonaceous aerosols and identifies their sources in three sites across southern Thailand: Surat-Thani, Hat-Yai, and Phuket, from June 2023 to May 2024. The findings highlight that PM 0.1 characteristics vary across different locations, primarily influenced by seasonal monsoons. In the upper south, including Surat-Thani and Phuket, PM 0.1 is significantly affected by air masses transporting pollutants from central Thailand and Cambodia during the northeast monsoon. The average PM 0.1 concentrations recorded were 1.43 ± 0.93 µg/m 3 in Surat-Thani and 0.71 ± 0.55 µg/m 3 in Phuket during this period. In contrast, in the lower south, particularly Hatyai, PM 0.1 is dominantly influenced by transboundary haze originating from Indonesian peatland fires, which is most pronounced during the southwest monsoon, with PM 0.1 concentrations reaching 1.43 ± 0.71 µg/m 3 during haze episodes. Organic carbon and elemental carbon were identified as the key contributors to PM 0.1 , with OC/EC ratios indicating distinct source contributions. The OC/EC ratio at Surat-Thani and Phuket was 2.68–3.52, suggesting contributions from both biomass burning and vehicle emissions, while at Hat Yai, the ratio was 3.77–4.69, indicating a dominant influence from biomass combustion. Principal Component Analysis further confirmed that biomass burning, engine exhaust, and secondary organic aerosols are the primary sources of PM 0.1 in the region. These findings provide crucial insights into how seasonal monsoons shape air pollution patterns in southern Thailand, emphasizing the need for targeted air quality management and mitigation strategies. Graphical Abstract