Size Distribution of Atmospheric Particles: 40-Year Trends and 20-Year Comparisons of Chemical Constituents between Residential and Roadside Areas in Osaka City, Japan

Abstract

Long-term observational data for the size distributions and particulate chemical components have been summarized to understand the past and current particulate conditions in Osaka City. The positive matrix factorization (PMF) method was also applied to estimate the source changes. The observational data obtained using Andersen cascade impactors reveals that for the 40 years from fiscal year (FY) 1976 to 2015, there was a 70% reduction in PMfine (less than 2.1 μm of the aerodynamic diameter) and 76% reduction in PMcoarse (over 2.1 μm). These correspond to a 71% and 74% reduction in PM2.5 (particulate matter less than 2.5 μm in diameter) and PM10-2.5, respectively. From the continuous chemical measurements made in this study, we observed a more than 50% reduction in coarse particulate elemental carbon (EC), SO42-, NH4+, Zn, Pb, and Cd, commonly in residential and roadside areas, over the last 20 years. Similarly, the level of the fine particulate EC, Ca2+, Cl-, Zn, Mg2+, Pb, and Cd was reduced by more than 50%. Notably, the results of the particulate component analysis of ECfine show a typical reduction of 73%-79% for 20 years, and this is the main component contributing to the reduction of atmospheric particulate concentration. However, there seems to have been no apparent reduction of Vfine concentrations, SO42-fine showed a relatively low reduction of 19% to 26%, and NH4+fine levels fell by 14% to 21% in 20 years. Since fine sulfate and ammonium have similar behaviors, ammonium sulfate is considered to be a secondary particle aerosol because of long-range transportation. The PMF analysis still estimates a high contribution rate of secondary particles, which is one of the current problems. In contrast, although vanadium is a minor element, it is likely to be generated from harbor areas with ships because they are susceptible to the prevailing sea breeze in summer. Therefore, in the future, it will be necessary to scrutinize and take countermeasures not only for long-range transportation but also for domestic sources.

Keywords

• elemental carbon (ec)
• long-term observation
• positive matrix factorization (pmf)
• sulfate
• vanadium