Inter-correlation of chemical compositions, transport routes, and source apportionment results of atmospheric PM2.5 in Southern Taiwan and the Northern Philippines

Abstract

This study investigated the inter-correlation of atmospheric PM2.5 between southern Taiwan and the northern Philippines. 24-hour samples of PM2.5 were simultaneously collected at two remote sites, Checheng (Taiwan) and Laoag (Philippines), during all four seasons. The water-soluble ions, metallic elements, carbonaceous content, and anhydrosugars in the PM2.5 were then analyzed to characterize the chemical fingerprint. Furthermore, principal component analysis, chemical mass balance (CMB) receptor modeling, and backward trajectory simulation were applied to resolve the source apportionment of PM2.5 at both of the sites. The results showed that Checheng and Laoag were highly influenced by polluted air masses transported long-range from the north, producing elevated PM2.5 concentrations during winter and spring. The water-soluble ions (WSIs) were abundant in secondary inorganic aerosols (SO4 2–, NO3–, and NH4+), which accounted for 34.1–76.0%. Crustal elements dominated the metallic content in the PM2.5, but the concentrations of trace elements originating from anthropogenic sources increased during the northwestern monsoon periods. More organic carbon (OC) than elemental carbon (EC) was found, with secondary OC (SOC) contributing approximately 23.9–38.9% to the former. Moreover, the level of levoglucosan highly correlated with those of K+ and OC, confirming that these three substances are key indicators of biomass burning. The two sites exhibited similar chemical compositions for PM2.5, indicating the possibility of transport between Checheng and Laoag, and a paired t-test obtained a p-value of 0.030 (p < 0.05), implying a potential inter-correlation for PM2.5 between southern Taiwan and the northern Philippines. The major sources of the PM2.5 were soil dust, mobile sources, sea salt, and biomass burning along the northerly transport routes during winter and spring. The contribution of anthropogenic sources (i.e., industrial boilers, waste incinerators, and secondary aerosols) to the PM2.5 frequently increased during winter and spring, unlike during summer, suggesting that the northerly transport of PM2.5 highly affected particulate air pollution at both of the sites.