Behavior of Airborne Particulate Secondary Pollutants in the Central Mountainous Area, Japan

Abstract

The behavior of the chemical components of suspended particulate mater (SPM) in a mountainous area were investigated. A special attention was paid on the seaconal and diurnal variations of the secondary particulate. The sampling site was Happo at an altitude of 1850m, in the centratl mountainous region of Japan.
Sulfate was the most abundant particulate and accounted for 20% of the SPM, followed by organic carbon (OC) (8%), NH₄⁺ (5%) and elemental carbon (EC) (4%). The concentrations of SO₄^2-were much higher from April to July than those from October to March, and these variations were similar to those of ozone, suggesting that almost all of the SO₄^2-was produced by the photo-oxidation of SO₂ and transported long distances. The ion balance between cations (NH₄⁺, Na⁺, Mg²⁺ and Ca²⁺) and anions (SO₄^2-, NO₃^-and Cl^-) tended toward anion excess, and equivalent concentrations of SO₄^2- were much higher than those of NH₄⁺ These results suggest that a portion of the SO₄^2-existed in the form of acidic aerosols such as HZSO₄ and NH₄HSO₄. Backward trajectory analysis suggected that the air pollutants in this mountainous area were transported not only from other regions of Japan, but also from continental Asia. Seasonal variations of T-NO₃ (total nitrate in gaseous and particulate matter), OC and oxalic acid concentrations were similar to those of ozone and SO₄^2-and the correlation coefficients with SO₄^2-were positive.These findings suggest that those components were produced by photochemical reactions. The secondary components, NH₄⁺, SO₄^2-, NO₃-and a part of the OC, accounted for more than 23% of the SPM from April to August.