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.
Highlights
The effects of fine particles (PM2.5) on human health and ambient air quality have attracted increasing global attentions for the past decades (Li et al 2016)
– no contribution to marine PM2.5. Both regular and intensive samplings of PM2.5 at the Matsu Islands showed that high PM2.5 concentrations were mostly observed in winter and spring, during the northeastern monsoon periods, while low PM2.5 concentrations commonly occurred in summer
It showed very likely that high PM2.5 concentration was mainly attributed to cross-boundary transport of PM2.5 emitted from anthropogenic sources from either neighboring Fuzhou City or upwind northern regions
Summary
The effects of fine particles (PM2.5) on human health and ambient air quality have attracted increasing global attentions for the past decades (Li et al 2016). Exposure to high PM2.5 level poses a considerable risk to health problems, such as aggravation of asthma, respiratory symptoms, and even cardiovascular and respiratory diseases (Anderson et al 1992; Dockery et al 1993). Long-term exposure to PM2.5 is highly associated with an increase in the risk of cardiopulmonary mortality by 6–13% per 10 μg/m3 of PM2.5 (Beelen et al 2008; Pope III et al 2002; Stanek et al 2011). In addition to human health, high PM2.5 concentration could cause poor ambient air quality, atmospheric visibility attenuation (i.e., regional haze), and global climate change and interfere with the earth’s radiation balance due to its complicated physicochemical characteristics of atmospheric PM2.5. Chemical composition (e.g., SO42− and NO3−) and size distribution (0.4–0.9 μm) of PM2.5 play a crucial role in atmospheric visibility degradation (Yuan et al 2002; Lee et al 2005; Yuan et al 2006)
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