Fine and ultrafine particle emission factors and new diagnostic ratios of PAHs for peat swamp forest fires.

Peatland fires are one of the major global sources of atmospheric particles. Emission factors for fine (PM1 and PM2.5) and ultrafine (PM0.1) particles and particle-bound polycyclic aromatic hydrocarbons (PAHs) from plants in the peat swamp forest (PSF), including Melaleuca cajuputi leaves, M. cajuputi branches, M. cajuputi bark, Lepironia articulata (Retz.) Domin, forest leaf litter and peat were measured in a laboratory combustion chamber. From these measurements, new PAH diagnostic ratios for fine and ultrafine particles were proposed for identifying the forest burning source. The new emission factors for PM were PM0.1: 0.03-0.33, PM1: 0.69-2.11 and PM2.5: 1.12-4.18 g/kg; for PM-bound PAHs, the factors were PM0.1: 5.7-166.0, PM1: 31.5-1338.9 and PM2.5: 36.3-3641.1 µg/kg. The predominant PAHs for PSF burning were Pyr, BbF, DBA (in PM0.1), Flu, DBA, BghiPe (in PM1), and BbF, DBA and BghiPe (in PM2.5). We also presented new diagnostic ratios for PSF burning, including BaP/(BaP + Chr): 0.39-0.75, BaP/(BaP + BbF): 0.21-0.47 and BaA/(BaA + Chr): 0.36-0.53. Moreover, the physical and chemical characteristics of ambient fine and ultrafine particles in the Kuan Kreng forest during the 2019 forest fire (FF) and 2021 non-forest fire (NFF) periods were investigated. The mean PM0.1, PM1 and PM2.5 concentrations during the FF period were approximately 3.5-4.4 times as high as those during the 2021 NFF period. New PAH diagnostic ratios of BaP/(BaP + BbF) versus BaP/(BaP + Chr) were able to identify PAH burning sources in PM1 and PM2.5 but were less clear for PM0.1, which was dominated by a single source - M. cajuputi. Chemical mass balance studies identified peat forest burning emissions as the main source of fine and ultrafine particles during the FF period. This study suggests that the new PAH diagnostic ratios can be used to identify the burning source for more precise source apportionment.

Source apportionment of PM2.5 in Thailand's deep south by principal component analysis and impact of transboundary haze.

Atmospheric particulate matter smaller than 2.5 micron (PM2.5) was evaluated at four sites in the lower southern part of Thailand during 2019-2020 to understand the impact of PM2.5 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 PM2.5 emission sources were identified by principal components analysis (PCA). The average mass concentrations of PM2.5 in the normal period, which represents clean background air, from four sites was 3.5-5.1 µg/m3, whereas during the haze period, it rose to 5.4-13.5 µg/m3. 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 PM2.5 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. SO42- 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.

Fine and ultrafine particle- and gas-polycyclic aromatic hydrocarbons affecting southern Thailand air quality during transboundary haze and potential health effects.

Distribution of PM0.1, PM1 and PM2.5 particle- and gas-polycyclic aromatic hydrocarbons (PAHs) during the 2019 normal, partial and strong haze periods at a background location in southern Thailand were investigated to understand the behaviors and carcinogenic risks. PM1 was the predominant component, during partial and strong haze periods, accounting for 45.1% and 52.9% of total suspended particulate matter, respectively, while during normal period the contribution was only 34.0%. PM0.1 concentrations, during the strong haze period, were approximately 2 times higher than those during the normal period. Substantially increased levels of particle-PAHs for PM0.1, PM1 and PM2.5 were observed during strong haze period, about 3, 5 and 6 times higher than those during normal period. Gas-PAH concentrations were 10 to 36 times higher than those of particle-PAHs for PM2.5. Average total Benzo[a]Pyrene Toxic Equivalency Quotients (BaP-TEQ) in PM0.1, PM1 and PM2.5 during haze periods were about 2-6 times higher than in the normal period. The total accumulated Incremental Lifetime Cancer Risks (ILCRs) in PM0.1, PM1 and PM2.5 for all the age-specific groups during the haze effected scenario were approximately 1.5 times higher than those in non-haze scenario, indicating a higher potential carcinogenic risk. These observations suggest PM0.1, PM1 and PM2.5 were the significant sources of carcinogenic aerosols and were significantly affected by transboundary haze from peatland fires. This leads to an increase in the volume of smoke aerosol, exerting a significant impact on air quality in southern Thailand, as well as many other countries in lower southeast Asia.

Impact of transport of fine and ultrafine particles from open biomass burning on air quality during 2019 Bangkok haze episode.

Transboundary and domestic aerosol transport during 2018-2019 affecting Bangkok air quality has been investigated. Physicochemical characteristics of size-segregated ambient particles down to nano-particles collected during 2017 non-haze and 2018-2019 haze periods were analyzed. The average PM2.5 concentrations at KU and KMUTNB sites in Bangkok, Thailand during the haze periods were about 4 times higher than in non-haze periods. The highest average organic carbon and elemental carbon concentrations were 4.6 ± 2.1 µg/m3 and 1.0 ± 0.4 µg/m3, respectively, in PM0.5-1.0 range at KU site. The values of OC/EC and char-EC/soot-EC ratios in accumulation mode particles suggested the significant influence of biomass burning, while the nuclei and coarse mode particles were from mixed sources. PAH concentrations during 2018-2019 haze period at KU and KMUTNB were 3.4 ± 0.9 ng/m3 and 1.8 ± 0.2 ng/m3, respectively. The PAH diagnostic ratio of PM2.5 also suggested the main contributions were from biomass combustion. This is supported by the 48-hrs backward trajectory simulation. The higher PM2.5 concentrations during 2018-2019 haze period are also associated with the meteorological conditions that induce thermal inversions and weak winds in the morning and evening. Average values of benzo(a)pyrene toxic equivalency quotient during haze period were about 3-6 times higher than during non-haze period. This should raise a concern of potential human health risk in Bangkok and vicinity exposing to fine and ultrafine particulate matters in addition to regular exposure to traffic emission.