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    Item type:Publication,
    Source apportionment of PM2.5 in Thailand’s deep south by principal component analysis and impact of transboundary haze
    (2023-08-01)
    Chaisongkaew, Phatsarakorn
    ;
    Dejchanchaiwong, Racha
    ;
    Inerb, Muanfun
    ;
    Mahasakpan, Napawan
    ;
    Nim, Nobchonnee
    Atmospheric particulate matter smaller than 2.5 micron (PM<inf>2.5</inf>) was evaluated at four sites in the lower southern part of Thailand during 2019–2020 to understand the impact of PM<inf>2.5</inf> transport from peatland fires in Indonesia on air quality during the southwest monsoon season. Mass concentration and chemical bound-PM, including carbon composition, e.g., organic carbon (OC) and elemental carbon (EC), polycyclic aromatic hydrocarbons (PAHs), and inorganic elements, were analyzed. The PM<inf>2.5</inf> emission sources were identified by principal components analysis (PCA). The average mass concentrations of PM<inf>2.5</inf> in the normal period, which represents clean background air, from four sites was 3.5–5.1 µg/m<sup>3</sup>, whereas during the haze period, it rose to 5.4–13.5 µg/m<sup>3</sup>. During the haze period, both OC and EC were 3.5 times as high as in the normal period. The average total PAHs and BaP-TEQ of PM<inf>2.5</inf> during the haze period were ~ 1.3–1.7 and ~ 1.2–1.9 times higher than those in the normal period. The K concentrations significantly increased during haze periods. SO<inf>4</inf><sup>2−</sup> dominated throughout the year. The effects of external sources, especially the transboundary haze from peatland fires, were significantly enhanced, because the background air in the study locations was generally clean. PCA indicated that vehicle emission, local biomass burning, and secondary particles played a key role during normal period, whereas open biomass burning dominated during the haze phenomena. This was consistent with the OC/EC and PAH diagnostic ratios. Backward trajectories confirmed that the sources of PM during the haze period were predominantly peatland fires in Sumatra, Indonesia, due to southwest wind.
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    Transboundary haze from peatland fires and local source-derived PM2.5 in Southern Thailand
    (2023-02-01)
    Promsiri, Preyapon
    ;
    Tekasakul, Surajit
    ;
    Thongyen, Thunyapat
    ;
    Suwattiga, Panwadee
    ;
    Morris, John
    This study characterizes impacts on PM<inf>2.5</inf> of transboundary haze from peatland fires in Indonesia and local emission sources during 2019–2020 to a large and densely populated city, Hat Yai in southern Thailand. Organic carbon (OC), elemental carbon (EC), water soluble organic carbon (WSOC), water soluble ions (WSI: Cl<sup>−</sup>, NO<inf>3</inf><sup>−</sup>, SO<inf>4</inf><sup>2−</sup> and NH<inf>4</inf><sup>+</sup>), element tracers (K, Na, Mg and Ca), heavy metals (Cr, Co, Pb, Cd, Ni, Mn) and As, and 16 polycyclic aromatic hydrocarbon (PAHs) components from PM<inf>2.5</inf> samples (n = 18) were measured to identify local and regional emission sources using a chemical mass balance (CMB) model. We used a combination of air mass backward trajectories and CMB source apportionment to identify PM<inf>2.5</inf> sources. An increase of PM<inf>2.5</inf> and chemical component concentrations, during the transboundary haze period, were clearly influenced by aerosols from open biomass burning in Indonesia: PAH concentrations were 2 times higher and OC concentrations, 5 times higher. Secondary organic carbons were predominant during transboundary haze periods, accounting for 52–58% of total OC, indicating higher secondary organic aerosol formation. High K levels demonstrated that the dominant source during this period was biomass burning. Whereas a high level of Ca in the background air came from urban road dust, as well as local biomass burning. Moreover, the increased concentration of SO<inf>4</inf><sup>2−</sup>, NH<inf>4</inf><sup>+</sup> and NO<inf>3</inf><sup>−</sup> during the wet season, as well as transboundary haze periods, was mainly derived the secondary inorganic aerosol formation. Effect on PM<inf>2.5</inf> concentration from a volcanic eruption near the air mass trajectory during the sampling period was minimal. However, it may have contributed slightly to an increase of SO<inf>4</inf><sup>2−</sup> concentration in PM<inf>2.5</inf>. Sources of PM<inf>2.5</inf> in Hat Yai were clearly influenced by local emission sources, e.g. diesel combustion and biomass burning (rubber wood and rice straw), transboundary haze and also secondary organic and inorganic aerosols.