Abstract: Background, aim, and scope Different sources of PM2.5 influence the chemical composition of airborne particles and ultimately, human health. Studies on the characteristics of water-soluble ions in PM2.5 have largely been conducted in inland areas, particularly for large and medium-sized cities. There are limited studies on water-soluble ions in PM2.5 for coastal cities. This study investigated the characteristics and sources of water-soluble ions in PM2.5 for Zhuhai, a typical coastal city in China. The study collected PM2.5 between June to December, 2016 to gain useful information and insights into pollution control strategies for local governments. Materials and methods PM2.5 samples were collected using a high-volume air sampler with a PM2.5 cutting head. Each sample was run for 48 h with quartz filter, where all filters were pre-combusted at 500℃. Filters were cut at 4 cm×4 cm to determine nine water-soluble ions by ion chromatography. Online data on meteorological parameters in Zhuhai were collected from the National Oceanic and Atmospheric Administration (NOAA). Results The concentrations of water-soluble ions in PM2.5 exhibited a significant seasonal variation, with levels in winter being higher than those in summer. The main components of PM2.5 were , , and , accounting for 85.07% of the total ion composition. From summer to winter, the proportion of and in ions decreased, while the proportion of increased. Discussion Based on cluster analysis of back trajectory, the seasonal variations in ion concentrations were associated with different air masses. The concentrations associated with terrigenous air masses in winter were higher than the ocean air masses in summer and autumn. Based on the charge balance between total anion and cation equivalents, PM2.5 is alkaline in summer and autumn and acidic in winter. The high concentration of , and in PM2.5 indicate that the level of secondary ions was relatively high. The mean ratio of / was 0.2, demonstrating that the main source of water soluble ions were stationary source emissions in Zhuhai. Principal factor analysis demonstrated that the mix of man-made sources with oceanic sources contributed 80.2% of the PM2.5 while agricultural sources contributed 16%. Ion and enrichment factor correlations implied the form and sources of ions. Conclusions Anthropogenic activities play an important role in PM2.5 ion concentrations in Zhuhai. PM2.5 is likely to be acidic in winter. Air mass transport plays a major role in PM2.5 ions concentration, particularly in winter. Recommendations and perspectives The government needs be attentive to the possibility of stationary source emissions from the air mass in Zhuhai in winter.
Keywords: urban heat island intensity; atmospheric fine particles; correlation analysis