Assessment of the Components and Sources of Acid Deposition in Northeast Asia: A Case Study of the Coastal and Metropolitan Cities in Northern Taiwan

In this study, temporal variations, major ion reference indexes, correlation analysis, and statistical data were used to investigate the chemical characteristics of the atmospheric pollutants in wet deposition and reasons for their formation, and further insight into the impact of local and regional atmospheric pollutant distributions on urban and coastal area environments. From November 2014 to October 2015, 158 rainwater samples were collected in coastal Wanli and urban Banqiao of southern Northeast Asia (northern Taiwan). The mean pH of the coastal and urban was 4.63 and 4.58, respectively, lower than the mean (5.31) of 10 East Asia regions during the year of 2015. This was possibly because the concentration of the combined SO42- and NO3- in the study area were greater than the mean of the 10 East Asian regions. This is verified by the calculation of sea-salt fraction (SSF) and non-SSF fraction (NSSF) in study areas, which indicated that Na+ and Cl- accounted for over 85% of the SSF, without Na+ in Banqiao, were mainly due to marine sources. For the NSSF, in addition to SO42- in Wanli, nearly 90% of wet disposition was from SO42- and NO3-, which were emitted from human activities. Furthermore, the analysis of fractional acidity (FA), neutralization factors (NF), neutralization potential (NP), and acidification potential (AP) revealed that acidified precipitation was caused by a lack of neutralizing compounds, which resulted in less neutralization of acidic precipitation. Finally, the results of correlation and principal component analysis (PCA) indicated that because coastal area were geographically closer to the ocean, wet deposition mainly comes from marine sources. However, in urban with a high population density and high traffic quantity, the ions in wet deposition primarily come from anthropogenic activities, such as industrial combustion and vehicle emissions.