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

Abstract

Abstract 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 − , NO 3 − , SO 4 2− , and NH 4 + were extracted to determine the concentration. In every size, the concentration of the five ions followed the order of SO 4 2− >NO 3 − ∼NH 4 + ∼Cl − >F − . Their concentrations in PM 1.6 were 5–7, 1–5, 3, 1–3, and ∼0.1 μg/m 3 , respectively, and occupied about 8–11%, 2–7%, ∼6%, 2–6%, and ∼0.1% of PM 1.6 mass, respectively. In PM 8 , about 70% of each ion existed in PM 1.6 , while in PM 3.7 , 50–80% was in PM 1.6 . The size distributions of SO 4 2− , NO 3 − , 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. NH 4 + showed a single fine mode peaking at 0.7 μm. Fine mode dominated the size distribution of SO 4 2− , NO 3 − , and NH 4 + . SO 4 2− , NO 3 − , Cl − , and NH 4 + had a good correlation in PM 1.6 between each other. But SO 4 2− strongly correlated to NO 3 − at every size stage. Comparison of size-fractionated equivalent ratios between [SO 4 2− ] and [NH 4 + ] suggested that the existing forms of SO 4 2− , NO 3 − , Cl − , and NH 4 + were probably (NH 4 ) 2 SO 4 , NH 4 NO 3 , and NH 4 Cl. [SO 4 2− ]/[NO 3 − ] 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.