Characterization of major water-soluble inorganic ions in size-fractionated particulate matters in Shanghai campus ambient air

The size-fractionated inhalable particles in ambient air were collected at the top of a lab building in a university campus of Shanghai; F−, Cl−, NO3−, SO42−, and NH4+ were extracted to determine the concentration. In every size, the concentration of the five ions followed the order of SO42−>NO3− NH4+ Cl−>F−. Their concentrations in PM1.6 were 5–7, 1–5, 3, 1–3, and 0.1 μg/m3, respectively, and occupied about 8–11%, 2–7%, 6%, 2–6%, and 0.1% of PM1.6 mass, respectively. In PM8, about 70% of each ion existed in PM1.6, while in PM3.7, 50–80% was in PM1.6. The size distributions of SO42−, NO3−, Cl−, and F− were characterized by bimodal types with fine mode peaking around 0.7 μm and coarse particle mode peaking around 3–5 μm. NH4+ showed a single fine mode peaking at 0.7 μm. Fine mode dominated the size distribution of SO42−, NO3−, and NH4+. SO42−, NO3−, Cl−, and NH4+ had a good correlation in PM1.6 between each other. But SO42− strongly correlated to NO3− at every size stage. Comparison of size-fractionated equivalent ratios between [SO42−] and [NH4+] suggested that the existing forms of SO42−, NO3−, Cl−, and NH4+ were probably (NH4)2SO4, NH4NO3, and NH4Cl. [SO42−]/[NO3−] ratio in fine mode was >1, which revealed that stationary source emission was still the important contributor to fine particles. The main sources of particulate inorganic ions were also discussed.