3.5 PAHs compounds based on fresh and aged aerosol data from laboratory chamber combustion of Malaysian peat, separated by two- and seven-day photochemical aging times simulated with an OFR. Although there was no significant difference in the weight percentage of LG in the PM mass between fresh (2.25 ± 0.016%) and two-day aged (2.28 ± 0.99%) samples, such a difference was observed83 between fresh (4.38 ± 0.50%) and seven-day aged (2.53 ± 0.19%) samples. For formic acid and oxalic acid, Chow et al.83 reported the weight percentages of formic acid and oxalic acid in the PM mass of fresh particles were 0.10 ± 0.014 and 0.26 ± 0.12%, respectively, and those after two days aging increased to 0.26 ± 0.049 and 1.14 ± 0.21%, respectively. After seven days aging, further increases in the weight percentage of formic acid (0.42 ± 0.10%) and oxalic acid (3.36 ± 0.28%) were revealed, indicating secondary organic aerosol (SOA) formation related to these compounds. Some studies5, 29 have measured the concentrations of PAHs in the gaseous and particulate phases, but not all phase concentrations were available, so the data were excluded. Saha et al.70 analyzed 36 PAHs, but in most cases, the concentrations of the US EPA 16 PAHs (see the “Appendix” sheet in the dataset) in PM during IPF- derived haze periods have been analyzed in field measurements. The concentrations of all 16 PAHs in PM2.5 (hereafter, “total PAHs level”) at receptor sites ranged from (a) 0.15 ng m-3 in Thailand120 to (b) 61 ng m-3 in Singapore the concentration rose to (c) 562 ng m-3 100 m away from the boundary of a peat fire in Riau Province of Sumatra, Indonesia28. The mass fractions of the total of the 16 PAHs in PM corresponding to cases (a), (b) and (c) were -1), respectively. The 30, 570 and 970 ppm (μg g-PM2.5differences in mass fraction suggest differences in haze intensity, as well as dilution and transformation, during transportation. The concentration varied significantly, depending on IPF intensity, distance from the emission source to the receptor site, meteorological conditions and local sources. (severe haze The total PAHs concentration increased during haze periods as compared with during non-haze periods. For example, the total PAHs level at Kuala Lumpur in Malaysia88 was 3.40 ng m-3 during the 2015 haze period, while the annual average concentration (including the haze period) was 2.04 ng m-3. In Singapore37, the total PAHs level increased from 24 ng m-3 during a non-haze period to 61 ng m-3 during a severe haze event in 2010. In Thailand, the average of total PAHs levels for four sites was 0.20 ng m-3 during the 2019 haze period and 0.13 ng m-3 in the non-haze period122 (Fig. S5 in the Supplementary Information). High molecular weight PAHs predominated in the haze period24, 88, 92, 119, 122. PAH congeners that increased in concentration during the haze Chemical Properties of the Southeast Asian Haze from Indonesian Peatland Fires in 2010)37. However, period were Acy, Ace, Flu, Phe, Flt, Pyr, BaA, Chr, BbF, BaP, Ind, BgP, and DhA (these abbreviations of congeners are spelled out in the “Appendix” sheet of the dataset) for Indonesian samples28. In Singapore37, an increase in congener concentrations was found for 13 congeners (Nap, Flu, Phe, Ant, Pyr, BaA, Chr, BbF, BkF, BaP, Ind, BgP and DhA) during the 2010 haze period. Among them, Pyr, Chr, BbF, BkF, BaP, InD and DBA levels were significantly higher than usual37. In Kuala Lumpur88, the dominant PAHs in PM2.5 were BbF, BkF, BaP, Ind and BgP during the 2015 haze event. In Thailand119, BkF, Act, DhA, BbF were the dominant congeners in the 2019 strong haze. Although the total PAHs concentration was specified, there were limited concentration data available on individual congeners (graphically depicted data only, or not indicated). Therefore, the difference in species between sampling sites was not significant. In laboratory experiments, the EF of total PAHs in PM10 from natural combustion of Indonesian peat was 20 mg kg-fuel-1, and the dominant congeners were Flu (11 mg kg-fuel-1), Phe (2.7), Pyr (1.5), Ant (1.1) and Flt (1.1)26. Sengupta et al.121 quantified the gas and PM EFs of 133 PAHs and their derivatives from smoldering combustion of Malaysian peat and Malaysian agricultural peat their chemical transformations during aging in an OFR. The EF of all 113 PAHs in fresh particles was 1.80 μg kg-fuel-1 and that in aged particles was reduced to 0.25 μg kg-fuel-1 for Malaysian peat. For fresh particles from the combustion of Malaysian peat, the dominant congeners were Phe (88.6 ng g-1), Flt (47.5) and BgF (20.8). In aged particles, the dominant congeners were Ace (20.2 ng g-1), Flt (20.1) and Phe (14.8). After oxidation of Malaysian peat combustion emissions in the OFR, the EF of three-ring particle-phase PAHs decreased by a factor of nearly eight121. (and PAH derivatives constitute a class of organic compounds derived from parent PAH structures with a variety of functional groups or elements. Typically they are nitrated (nitro) PAHs (NPAHs), oxygenated PAHs (OPAHs), halogenated PAHs (XPAHs) or alkylated PAHs (APAHs) (Peng et al., 2023). In field measurements, only OPAHs were quantified, and the concentrations of the congeners were in the range of 0.03 to 4.46 ng m3 during the 2006 haze period in Singapore29, but the data were the sum of the gas- and TSP-phase OPAHs. Particulate OPAHs were analyzed in the two laboratory experiments mentioned in the above paragraph26, 121. No OPAHs were detected in the experiment by Sengupta et al.121, but Iinuma et al.26 quantified the EF of 9-fluorenone (0.75 ng g-1) and 9,10-anthracenedione (0.29). In our survey, no other derivatives aside from OPAHs were found. Diagnostic ratios were used for source apportionment of ambient PAHs in PM2.5 collected in Bangi, Malaysia during the southwest monsoon (including haze) in 201351, four other fuels), and 43

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