||In recent years, due to rapid economic and industrial development of mainland China, significant increases in fossil fuel consumption and anthropogenic emissions of air pollutants cause increasing environmental pollution problems. Matsu Islands located at the Minjiang Estuary faces Fuzhou in mainland. The islands have no large-scale industries and pollution sources, which conserve the islands as an ecological environment. However, the ambient air quality is worse than the rural areas of Taiwan, and even more serious than urban air quality. Due to the unique meteorological and geographical environment, Matsu and Fuzhou areas surrounding the Minjiang Estuary are treated at the same air quality zone for investigating their sources of suspended particles.|
In this study, six sites were selected to collect PM10 samples from July 2012 to April 2013, respectively located at offshore (Matsu) and inland (Fuzhou) region for different seasons. The chemical composition of PM10 was then analyzed to characterize the PM10 sampled at inland and offshore regions. Additionally, in order to clarify the region's pollution sources and their contributions, this study applied principal component analysis (PCA), chemical mass balance (CMB) receptor model, and backward trajectory simulation methods to understand the source apportionment of suspended particles, and to explore their variation for different seasons.
The results showed lower average PM10 concentration in summer, and higher concentration in the northeast monsoon period. From the perspective of spatial distribution, PM10 concentration increased from the west to the east. The PM10 concentrations observed at MH site were generally higher than other sites for all seasons. However, the spatial distribution of PM10 was inconsistent with the seasonal prevailing wind direction, showing that ambient PM10 at Minjiang Estuary was not only influenced by long-range transportation, but also by local emissions from Fuzhou.
Chemical composition analysis showed that most abundant water-soluble ionic species of PM10 were secondary inorganic aerosols (SO42-, NO3-, and NH4+) which accounted for 70% of total ions, resulting in NR of suspended particles less than unity at Minjiang Estuary. These results indicated that the upwind acidic pollutants transferred to the Minjiang Estuary, making rendered acidic aerosols. For all seasons, the major metallic elements of suspended particles were Al, Ca, Fe, K, Mg, other trace metals (eg: Cd, As, Ni and Cr) concentration increased during the northeast monsoon period. Organic carbons (OC) was the main species of carbon for all seasons, thus OC/EC ratio was generally higher than 2.2. The spatial distribution showed that metallic elements and carbon components had relatively higher concentrations at inland than those at offshore.
Results from PCA and CMB receptor model showed that major sources of ambient PM10 at Minjiang Estuary were soil dusts, secondary inorganic aerosols, transportation emissions, sea salts, and biomass burning. During the northeast monsoon and poor air quality periods, the contribution of industrial pollution grew eight times, and cross-boundary transportation accounted for 55~77% of total PM concentrations, showing that ambient air quality was significantly affected by cross-boundary transport at Minjiang Estuary.