Characteristics and Sources Apportionment of Fine Particulate Matter in a Typical Coastal City During the Heating Period

To clarify the pollution characteristics and sources of PM2.5 in Weihai during the heating period, PM2.5 samples from ambient air were collected at three routine air quality monitoring sites from January to March 2018. The OC, EC, water-soluble ions, and elements in PM2.5 were analyzed, and the sources of PM2.5 were identified using the PMF model. The results showed that the average daily mass concentration of PM2.5 was (33.80±22.45) μg·m-3, and the NO3-, NH4+, SO42-, OC, and EC were the main components of PM2.5. As a coastal city, the Cl- ratio was relatively high in PM2.5. Meanwhile, the compositions of PM2.5 were affected by the emission of pollutants with local industrial characteristics. Both NO3-/SO42- and OC/EC showed that mobile sources had a high contribution during the heating period. The acid-base ions in water-soluble ions showed that PM2.5 is weakly alkaline, and NH4+ is excessive. NH4+ mainly existed in the form of NH4NO3 and (NH4)2SO4. During the polluted period, the concentration of secondary pollutants significantly increased, and the mass concentrations of NH4+, NO3-, SO42-, OC, and EC were 4.21, 5.27, 3.23, 2.02, and 1.81 times that of the cleaning period, respectively. The PMF model showed that secondary aerosols were the major source of PM2.5, accounting for 32.4%-36.0% of PM2.5. The contributions of vehicle exhaust, coal combustion, biomass burning, and dust were 15.6%-18.9%, 12.1%-17.8%, 9.0%-10.4%, and 8.6%-11.3%, respectively, while the contributions of process emission (2.1%-8.3%), non-road mobile sources (2.4%-3.7%), and sea salt (3.5%-5.6%) were less.