Characteristic of Size-Classified Airborne Particulates in Kobe, Japan

Abstract

Airborne particulate samples were collected and fractionated into five sizes (diameter of < 1.1, 1.1-2.0, 2.0-3.3, 3.3-7.0, > 7.0 μm) with a high volume cascade impactor. The size distribution of airborne particulates was bimodal, having two peaks, coarse (> 7.0 μm) and fine (< 1.1 μm), which accounted for approximately 29% and 42%, respectively. Inhalable particulates accounted for approximately 50% of the total. The mass percentages of these extracts were also similar to airborne particulate concentrations. Eight authentic polycyclic aromatic hydrocarbons (PAHs; fluoranthene, pyrene, benz[a]anthracene, benzo[e]pyrene, benzo[b]fluoranthene, benzo[k] fluoranthene, benzo[a]pyrene, benzo[ghi]pelyrene) were detected in airborne particulates. The concentration of PAHs was dependent on size, with the following order: airborne particulates larger than 7.0 < 3.3-7.0 < 2.0-3.3 < 1.1-2.0 < smaller than 1.1 μm. Almost all of the PAHs detected existed in fine airborne particulates smaller than 1.1 μm. Ionic species in size-classified airborne particulate were also investigated. NH₄⁺, SO₄^2- and K⁺ existed in the fine particulates, whereas NO₃^-, Cl^- and Na⁺ existed in the coarse particulates. It is likely that SO₄^2- and NO₃^- were generated from the combustion of fossil fuel and air, and Na⁺ and Cl^- from sea salt. Since NO₃^- was generated from atmospheric NO₂, these concentrations were related to each other. The sampling site is located near a highway, so the results suggested that the main source of most fine particulates was car exhaust, especially diesel exhaust.