Size-segregated distribution of ambient particulate matter (PM) was determined using a micro-orifice uniform deposition impactor (MOUDI) and a nano-MOUDI in southern Taiwan. Eleven water-soluble ionic species including six anions (NO3-, SO4(2-), Cl-, F-, NO2-, Br-) and five cations (NH4+, Na+, K+, Ca2+, Mg2+) for particulate inorganic ions and five gaseous pollutants (i.e., HNO2, HNO3, HCl, SO2, NH3) were analyzed during episode and non-episode periods. The particulate mass concentration was about 30 microg/ m3 higher at night than during the day, and it reached 162 microg/m3 during the episode periods. The difference was mainly attributable to the particle size of 0.1-2.5 microm. Nitrate, sulfate, ammonium, and chloride ions were the dominant inorganic ions in PM. HONO and NH3 concentrations were high at night; in contrast, HNO3, HCl, and SO2 were high during the day. The equivalent ratio of {[NO3-] + 2 [SO4(2-)}/[NH4+] was about 0.98 and revealed a high correlation between {[NO3-] + 2[SO4(2-)]} and [NH4+] that clearly pointed to ammonium neutralization or condensation of ammonium nitrate and ammonium sulfate in PM0.32. The precursor gases and ionic species in different particle sizes did not reveal a strong correlation, which could be attributed to the complex of source emissions, atmospheric reactions and meteorological parameters in the area.
Implications: Size-segregated distribution and chemical compositions of atmospheric aerosols play important roles in their visibility reduction, health effects, and toxicity in urban areas. Inorganic ionic species are major constituents in particulate matter, except carbonaceous chemicals. In this work, the compositions of water-soluble ions in particulate matter and acid/base gaseous pollutants (such as HNO2, HNO3, HCl, SO2, NH3) were determined during the day and at night during episode and non-episode periods from 2006 to 2007 in southern Taiwan.