||In recent years, the rapid economic and industrial development of mainland China has significantly increase the consumption of fossil fuel and anthropogenic emissions of air pollutants causing high environmental pollution problems. Although the Matsu Islands have no large-scale industries and pollution sources, which conserve the islands as an ecological environment. However, the ambient air quality is worse possibly due to long-range transportation during the northeastern monsoon period. |
This study selected four PM2.5 sampling sites (Nankan, Beigan , Donyin, and Chukuang) located at offshore Islands of the Matsu Islands. PM2.5 sampling was conducted in daytime (8:00-20:00) and nighttime (20:00-08:00) at NK site, which included regular and intensive sampling. Regular sampling was conducted to collect PM2.5 from June 2014 to May 2015, while intensive sampling was conducted to collected PM2.5 with BGI-PQ200 and particle size distribution with a MOUDI at NK site for 5 consecutive days during the poor air quality period. Additionally, in order to clarify the region's pollution sources and their contributions, this study further selected major emission and stationary sources to collected PM2.5 for chemical analysis, which coordinated chemical mass balance (CMB) receptor model to understand the source apportionment of suspended particles.
The results indicated that the lowest average concentration of PM2.5 were observed in the summer. The PM2.5 concentration significantly increased during the northeastern monsoon period. From the perspective of spatial distribution. it showed that PM2.5 concentration decreased from west to east, and BG site was generally higher than other sites in all seasons. Field measurement results showed that PM2.5 concentrations at the Donyin Islands (DY) in different seasons were always lower than other sampling sites.
Chemical composition analysis showed that most abundant water-soluble ionic species of PM2.5 were secondary inorganic aerosols (SO42-, NO3-, and NH4+) which accounted for 70% of total ions. The metallic elements Al, Ca, Fe, K, Mg dominated the chemical species of particles, other trace metals (eg, Zn, Pb, Cr, Ni, As, and Cd) concentration increased during the northeastern monsoon periods. The daytime and nighttime PM2.5 concentration ratios (D/N) for Zn, Pb, Cr, Ti, and Mn were varied a larger range, indicating that the emission sources of PM2.5 were different in daytime and at nighttime. Organic carbons (OC) were the main species in all seasons, and OC/EC value was between 1.64-3.78.
Results obtained from PCA and CMB receptor modeling showed that major sources of PM2.5 in the Matsu Islands were soil dusts, Fuel Boiler, sea salt and secondary inorganic aerosols. During the northeastern monsoon periods, the major transportation routes were northern transportation (N-type) and anticyclonic outflow (AO-type), in which pollution sources and their contribution were higher during these period. The trend of industrial pollution was higher in the daytime while secondary inorganic aerosols was oppsite. Agricultural burning in winter and spring was generally higher than other sources, which contributed 8.85-9.32% of PM2.5. Overall, cross-boundary transport accounted for 28~68%, showing that the Matsu Islands was significantly influenced by the cross-boundary transport.