Parallel continuous observation of submicron particle (PM₁) and PM_2.5, and characterization of PM₁ in a suburban of Tokyo

Abstract

Parallel observations of the PM₁, submicron particles and PM_2.5 were carried out for four years from April 2005 in order to characterize the PM₁ in a suburb of metropolitan Tokyo. The PM₁ sampler was made using a Sharp cut cyclone (SCC). The PM₁ annual mean concentrations were in the range of 15.5-18.3 μg m^-3 and those of PM_2.5 were 19.4-22.5 μg m^-3. The PM₁ weekly mean concentrations had a high correlation with those of PM_2.5 (r = 0.92, n = 186) , and the ratios of PM₁ to PM_2.5 (PM₁/PM_2.5) were 0.84±0.11. The major chemical components of PM₁ were also compared to those of PM_2.5. The PM₁/PM_2.5 of NH₄⁺, SO₄^2-, and TC were almost constant and higher, 0.74-0.88 for the entire year. On the other hand, the ratios of Na⁺, Mg²⁺ and Ca²⁺ were variable. The lowest ratios of Mg²⁺ and Ca²⁺ were observed in the winter. Some of the surface soil particles floated by strong winds from the dry paddy and field after the harvest should be contained in the PM_2.5. While the correlation coefficients of NH₄⁺, Cl^-, NO₃^-, SO₄^2- and TC between PM₁ and PM_2.5 were greater than 0.90, those of Mg²⁺ and Ca²⁺ were particularly low, i. e., 0.17 and 0.10. The slope of the linear regression formula of Ca²⁺ was extremely low, i. e., 0.02. This means that PM₁ was not affected by the coarse particles contained in the PM_2.5. As a result, PM₁ was more suitable than PM_2.5 as an indicator to the evaluate fine particles from anthropogenic sources.