Abstract
This study characterized the PM2.5 in terms of its spatial distribution, chemical composition, and seasonal/diurnal variation on the Matsu Islands in the northern Taiwan Strait. The PQ-200 samplers were employed to conduct simultaneous 24-h seasonal measurements of PM2.5 on four offshore islands, viz., Nankan Island (Site NK), Beigan Island (Site BG), Dongyin Island (Site DY), and Chiukung Island (Site CK) as well as 12-h diurnal measurements for both regular and intensive samplings, and 24-h episodic measurements at one of the locations (Site NK). Additionally, the chemical signatures of PM2.5 collected at six predominant local sources were established via chemical analysis, which coordinated as source profiles for chemical mass balance (CMB) receptor model to resolve the source apportionment of PM2.5. Of the four seasons, summer exhibited the lowest average PM2.5 concentration. In winter and spring, the level of PM2.5 significantly rose under the influences of Asian Northeastern Monsoons (ANEMs). Furthermore, the spatial distribution of PM2.5 across the islands showed a tendency to gradually decrease from the west to the east, with the Site NK always displaying the highest value regardless of the season. In general, the chemical composition primarily consisted of water-soluble ions (WSIs) owing to the abundancy of secondary inorganic aerosol (SIA) which accounted for 69.8% of the WSIs and 45.5% of the PM2.5. Crustal elements dominated the metallic components, although the content of trace metals increased in both concentrations and proportion during the ANEMs. Organic carbon (OC) dominated the carbonaceous content of PM2.5 in all seasons, with OC/EC values ranging from 1.64 to 3.78. During the episodes of poor air quality, the majority of incoming air masses followed a northern transport route (N-route) or an anticyclonic outflow route (AO-route) transported from the continent to the islands. The CMB receptor modeling results showed that the major sources of PM2.5 on the Matsu Islands were road dust, industrial boilers, secondary aerosols, vehicular exhausts, and sea salts. Overall, the PM2.5 pollution was originated from both local and remote sources, with 28~68% of the PM2.5 concentrations arising from long-range transport.
Highlights
With vigorous economic development, industrialization and urbanization of East Asian countries had become more prosperous and densely populated, which lead to the increases of both energy consumption and air pollution emission (Xu et al, 2020a)
While watching the spatial distribution trend more closely, we found that a spatial distribution trend of PM2.5 concentrations decreasing from the north to the south in fall and winter, while an opposite spatial variation trend was observed from the south to the north in spring and summer
The results indicated that the highest PM2.5 concentrations mostly occurred for the Nroute originating from Siberia, Mongolia, northern China, and passing along the coastal region of eastern China that mainly occurred from early fall to early spring (Fig. 6(a))
Summary
Industrialization and urbanization of East Asian countries had become more prosperous and densely populated, which lead to the increases of both energy consumption and air pollution emission (Xu et al, 2020a). China has experienced fast economic and industrialized development, resulting in severe environmental problems, poor regional air quality. One of the most important air pollution issues concerned by general publics is regional hazes which frequently occurred in China are commonly accompanied with monsoons and could transport regionally and even. Combustion is one of the most important processes that generate fine particles. In addition to industrial combustion process, biomass burning such as slash-and-burn, and bush and forest fires could emit huge amounts of fine particles to the atmosphere (Ramanathan et al, 2007).
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