||In recent years, the rapid economic and industrial development of East Asia has significantly increased the consumption of fossil fuel and the emissions of anthropogenic sources causing severe environmental problems. Furthermore, biomass burning often occurs in southeastern Asia and southwestern China in spring. The ambient air quality becomes worse possibly due to long-range transport from Chinese haze during the northeastern monsoon periods. The objectives of this study was to collect PM2.5 at intersection of Bashi Channel, Taiwan Strait, and South China Sea, characterize their chemical fingerprint, and identify their potential sources and contributions.|
This study collected PM2.5 in four seasons from July 2016 to March 2017 at Che-cheng (Taiwan), Laoag (Philippines), and Dongsha Islands (South China Sea) simultaneously. After sampling, Conditioning, and Weighing, water-soluble ionic species, metallic elements, carbonaceous contents, anhydrosugars, and organic acids of PM2.5 were then analyzed to figure out the chemical fingerprint of PM2.5 sampled at Che-cheng, Laoag, and Dongsha Islands. Furthermore, chemical mass balance (CMB) receptor modelling and backward trajectory simulation were further used to identify the potential sources of PM2.5 and their contributions in different seasons.
Field measurement results showed that high PM2.5 concentrations were observed in winter and spring. During the northeastern monsoons periods, the impacts of Asian dusts, biomass burning, and Northeast Monsoons on ambient air quality commonly occurred, which lead high PM2.5 contributions from long-range transport toward the target area. From the perspective of diurnal variation, we found that showed that PM2.5 concentration in the daytime was generally higher than those at nighttime except in winter at all sites.
Chemical analysis showed that the most abundant water-soluble ionic species of PM2.5 were secondary inorganic aerosols (SO42-, NO3-, and NH4+) which accounted for 50.7~71.5% of total ions. The metallic elements K, Ca, Mg, Fe, and Al dominated the chemical species of PM2.5, while the concentrations of other trace metals (eg: Cd, A, Ni, and Cr) increased during the northeastern monsoon periods. Organic carbon (OC) was the main carbonaceous species in all seasons, and OC/EC ratios and secondary organic carbon (SOC) increased during the northeastern monsoon periods. The levoglucosan concentrations in summer and fall were commonly lower than those in winter and spring, showing that PM2.5 concentrations were highly influenced by biomass burning in winter and spring. In spring, three sampling sites were influenced by long-range transport and biomass burning since the concentrations of levoglucosan in spring were higher than other seasons. Oxalic acid was the most abundant organic acid, and followed by succinic acid and malonic acid. Organic acids of PM2.5 at Laoag were commonly higher than those at Che-cheng and Dongsha Islands. The mass ratio of malonic and succinic acids (M/S ratio) in PM2.5 showed that PM2.5 were mainly attributed by secondary organic aerosols. High M/S ratios in this study showed that PM2.5 was mainly contributed from secondary organic aerosols. Daytime organic acid concentrations were always higher than nighttime organic acid concentration except in winter.
Results obtained from CMB receptor modeling showed that major sources of PM2.5 at three sites were sea salts, fugitive dusts, mobile sources, secondary sulfate, biomass burning, secondary nitrate. The concentration trend of biomass burning increased since fall. Overall, long-range transport accounted for 41~80%, 26~75%, and 25%~83% in Checheng, Laoag, and Dongsha Islands, showing that the three sampling sites was significantly influenced by the long-range transport. It was similar to our past researches that the average long-range transport distributions accounted for 44.9%, 57.3%, and 39.8% at the west-side sites, east-side sites, and offshore site of the Taiwan Strait, respectively (Li et al., 2016).
The trend of mobile sources, biomass burning, industrial process, boilers, incinerator, and steel plants was generally higher in the daytime than those of nighttime. Biomass burning in winter and spring contributed were than in other seasons.