Measurement of atmospheric particles and anionic species across central Taiwan

The ambient air concentrations and fluxes of various anionic species were sampled by MOUDI, TSP and dry deposition plates at a traffic sampling site in Taichung, central Taiwan. In the sampling period, from September to December 2000, the ambient air particle concentrations (PM₁, PM_2.5, PM₁₀ and TSP) were lower in the September than in the other three months (October to December). The reason is that the northwest wind brought more particles (diameter less than 10 μm) and the higher wind speed caused higher dry deposition fluxes and TSP concentrations in the last three months. The anion species percentages of TSP were 0.24%, 13.7%, 0.52%, 12.0%, 18.9% and 54.6% for F^-, Cl^-, Br^-, NO₂ ^-, NO₃ ^- and SO₄ ^2-, respectively. The results revealed that SO₄ ^2-, NO₃ ^-, Cl^- and NO₂ ^- were the dominant species at the traffic sampling site. The ion-size distributions of Cl^-, NO₂ ^- and NO₃ ^- were unimodal, the main peak being between 3.2 and 5.6 μm. In contrast, the size distribution of SO₄ ^2- was bimodal, with the main peaks in the particle size ranges 0.32-0.56 μm and 3.2-5.6 μm. The ambient average particle dry deposition flux was 6.28 μg/m²/s, and the dry deposition fluxes were 0.01, 94.6, 0.05, 34.7, 72.2 and 376.4 ng/m²/s for F^-, Cl^-, Br^-, NO₂ ^-, NO₃ ^- and SO₄ ^2-, respectively. The dry deposition velocities were 3.10, 0.03, 3.67, 0.05, 1.54, 2.03 and 3.67 cm/s for F^-, Cl^-, Br^-, NO₂ ^-, NO₃ ^- and SO₄ ^2-, respectively.