Mass-size distributions of particulate sulfate, nitrate, and ammonium in a particulate matter nonattainment region in southern Taiwan

Concentrations and distributions of three major water-soluble ion species (sulfate, nitrate, and ammonium) contained in ambient particles were measured at three sampling sites in the Kao-ping ambient air quality basin, Taiwan. Ambient particulate matter (PM) samples were collected in a Micro-orifice Uniform Deposit Impactor from February to July 2003 and were analyzed for water-soluble ion species with an ion chromatograph. The PM₁/PM_2.5 and PM₁/PM₁₀ concentration ratios at the emission source site were 0.73 and 0.53 and were higher than those (0.68 and 0.48) at the background site because there are more combustion sources (i.e., industrial boilers and traffic) around the emission source site. Mass-size distributions of PM NO₃⁻ were found in both the fine and coarse modes. SO₄²⁻ and NH₄⁺ were found in the fine particle mode (PM_2.5), with significant fractions of submicron particles (PM₁). The source site had higher PM₁/PM₁₀ (79, 42, and 90%) and PM₁/PM_2.5 concentration ratios (90, 58, and 93%) for the three major inorganic secondary aerosol components (SO₄²⁻, NO₃⁻, and NH₄⁺) than the receptor site (65, 27, and 65% for PM₁/PM₁₀; 69, 51, and 70% for PM₁/PM_2.5). Results obtained in this study indicate that the PM₁ (submicron aerosol particles) fraction plays an important role in the ambient atmosphere at both emission source and receptor sites. Further studies regarding the origin and formation of ambient secondary aerosols are planned.