||This study aims to investigate the spatiotemporal distribution, chemical characteristics, source apportionment, and the contribution of transportation routes of atmospheric fine particle (PM2.5) over the coastal, sea, and offshore areas of the Taiwan Strait. Fine particles (PM2.5) were simultaneously collected at six sites including two sites (Xiamen and Fuzhou) on the west-side of the Taiwan Strait, one site (Penghu Islands) at an offshore site, and three sites (Kaohsiung, Taichung, and Taipei) on the east-side of the Taiwan Strait in the years of 2013-2015. |
Field sampling of PM2.5 at large scale coastal and islands areas around the Taiwan Strait indicated that the average PM2.5 concentrations at the west-side sites were generally higher than those at the east-side sites, while those increased significantly from the north sites to the south sites at both sides of the Taiwan Strait, respectively. PM2.5 and PM2.5-10 concentrations in winter and spring were generally higher than those in summer and fall. The most abundant chemical composition were secondary inorganic aerosols (SO42-, NO3-, and NH4+), natural crustal (Mg, Ca, AL, K, and Fe), and anthropogenic metals (Pb, Ni, and Zn). Moreover, high OC/EC ratios of PM2.5 were commonly observed at the west-side sites located at the downwind of major stationary sources, such as utility power plants, petrochemical plants, and industrial complexes.
Results obtained from the transportation routes and potential sources of PM2.5 at the Taiwan Strait, clustered transportation routes based on backward of trajectory simulation indicated that PM2.5 could be transported from North China, eastern coast of China, Korea Peninsula, or South Japan, suggesting that it was mainly attributed to the combination of the relatively elevated emissions from fossil fuel (e.g. coals) combustion and biomass (e.g. woods) burning for space heating, long-range transport (LRT) of air pollutants. Results obtained from CMB receptor modeling showed that the source apportionment of secondary sources were in order of east-side sites > offshore site > west-side site, suggesting aged secondary particles could be formed during the transportation process by long longer range and duration toward the east-side sites and the offshore site. Result obtained from cross-boundary contributions of PM2.5 around the Taiwan Strait showed that the average cross-boundary transportation contributions 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.
Results obtained from the chemical characteristics over sea and offshore site in the Taiwan Strait for sampling cruises indicated that fine particles were generally higher than those of coarse particles over sea than those at the offshore site. Moreover, the contributions of nss-WSI for PM2.5 at the offshore site were obviously higher than those over sea, while the contributions of ss-WSI for PM2.5 at the offshore site were generally lower than those over sea during the high pollution episodes seasons.
The simulated surface wind fields showed that northerly winds blew atmospheric particles from long-range transportation toward the northwestern Taiwan Strait in the Matsu Islands domain, while high pressure anticyclonic systems caused the accumulation of atmospheric particles at the Xiamen Bay in the Kinmen Islands domain, and the prevailing winds and sea-land breezes highly influenced the surface wind fields over the island and coastal regions caused by the combination of local sources and northward long-range transportation in the Penghu Islands domain.