Chemical characteristics, source apportionment, and regional transport of marine fine particles toward offshore islands near the coastline of northwestern Taiwan Strait

Abstract

This study aims to investigate the spatiotemporal variation, chemical composition, and source apportionment of marine fine particles (PM2.5) as well as their regional transport toward the Matsu Islands located near the coastline of northwestern Taiwan Strait. Four offshore island sites located at the Matsu Islands were selected to conduct both regular and intensive sampling of marine PM2.5. Water-soluble ionic species, metallic elements, and carbonaceous contents were then analyzed to characterize the chemical characteristics of marine PM2.5. In order to identify the potential sources and their contributions to marine PM2.5, chemical mass balance (CMB) receptor model was employed along with the backward trajectory simulation to resolve the source apportionment of marine PM2.5 and to explore their transport routes in different seasons. The results showed that high PM2.5 concentrations were commonly observed during the northeastern monsoon periods. Additionally, marine PM2.5 concentration decreased from the west to the east with the highest PM2.5 at the Nankang Island and the lowest PM2.5 at the Donyin Island in all seasons, indicating an obvious concentration gradient of PM2.5 transported from the continental areas to the offshore islands. In terms of chemical characteristics of PM2.5, the most abundant water-soluble ions of PM2.5 were secondary inorganic aerosols (SO42−, NO3−, and NH4+) which accounted for 55–81% of water-soluble ions and 29–52% of marine PM2.5. The neutralization ratios of PM2.5 were always less than unity, indicating that NH4+ cannot solely neutralize nss-SO42+ and NO3− in marine PM2.5 at the Matsu Islands. Although crustal elements (Al, Ca, Fe, K, and Mg) dominated the metallic content of marine PM2.5, trace anthropogenic metals (Cd, As, Ni, and Cr) increased significantly during the northeastern monsoon periods, particularly in winter. Organic carbons (OCs) were always higher than elemental carbons (ECs), and the mass ratios of OC and EC were generally higher than 2.2 in all seasons, implying that PM2.5 was likely to be aged particles. During the poor air quality periods, major air mass transport routes were the northern transport and the anti-cyclonic circulation routes. Source apportionment results indicated that fugitive soil dusts and secondary aerosols were the major sources of marine PM2.5 at the Matsu Islands, while, in winter, biomass burning contributed up to 15% of marine PM2.5. This study revealed that cross-boundary transport accounted for 66~84% of PM2.5 at the Matsu Islands, suggesting that marine PM2.5 at the Matsu Islands has been highly influenced by anthropogenic emissions from neighboring Fuzhou City as well as long-range transport from Northeast Asia.

Seasonal Variations of Marine Environment and Primary Production in the Taiwan Strait

“…The areas that are framed by blue lines are designed to be offshore wind farms. The Changyun Rise is between 119.5-120.1 • E and 23.9-24.6 • N, where the water depth shallower than 50 m. Schematic showing the Taiwan Strait circulation in (a) winter, (b) spring, (c) summer, and (d) autumn (water currents were taken from Jan et al, 2002).…”

“…Wind stress explains a majority of the transport reversals (Ko, 2003). As the wind directions have changed, the transportations and circulations of water masses in the Taiwan Strait have changed (Jan et al, 2002(Jan et al, , 2006(Jan et al, , 2010Chen, 2003Chen, , 2011Chen and Sheu, 2006;Wu et al, 2007;Chen et al, 2010). The wind fields over the strait are southwesterly dominated in summer and northeasterly dominated in winter.…”

“…Additionally, tropical storms and typhoons also influence this area during the summer via induced heavy rainfall, strong vertical water mixing or upwelling (Ko et al, 2016). Jan et al (2002) pointed out that the deep Penghu Channel guides the intruding KBW northward into the Changyun Rise (CYR) and partially blocks along-strait transport on the eastern side of the strait in winter. On the other hand, the MCCW is conveyed by the northeast monsoon-driven flow to the northern Taiwan Strait during the winter (Jan et al, 2002).…”

“…Jan et al (2002) pointed out that the deep Penghu Channel guides the intruding KBW northward into the Changyun Rise (CYR) and partially blocks along-strait transport on the eastern side of the strait in winter. On the other hand, the MCCW is conveyed by the northeast monsoon-driven flow to the northern Taiwan Strait during the winter (Jan et al, 2002). In addition, Jan et al (2010) found that the source water in the Taiwan Strait comes from the SCSW in summer.…”

Seasonal Movement Patterns of the Bigfin Reef Squid Sepioteuthis lessoniana Predicted Using Statolith δ18O Values

“…However, the individuals of the autumn group had a high probability (>0.8) of hatching in the waters of southern and southwestern Taiwan (i.e., the Penghu Islands). The paralarvae were transported northward by the Kuroshio Current or the South China Warm Current into the Taiwan Strait during September and October (Tang et al, 2000;Jan et al, 2002Jan et al, , 2006. Although the results suggest that waters at a depth of 100 m near the coast of southern Taiwan are also potential hatching grounds, adult females are unlikely to have laid eggs at a depth of down to 100 m because the environment is unsuitable for planktonic paralarvae and Distribution of juvenile individuals appeared to be widespread around Taiwan, both horizontally and vertically.…”