Abstract
Atmospheric particulate matter (PM) and its chemical components were monitored at the rooftop of a building in the central Tokyo metropolitan area from FY 1994 to FY 2004. Size-separated PM samples were collected as PM21-7, (2.1-7μm) and PM2.1 (<2.1μm). The PM7 (<7μm) concentration was constant at about 50μgm-3 in the late 1990s, but showed a decreasing trend fmm 2000 onward. The ratio of PM21 to PM7 decreased simultareously with PM21 concentration. Carbonaceous components that were determined by a thermal method were conected by linear regression equation of those values against results determined by a thermal/optical method. Elemental carbon (EC) was the main component of PM; 90% of it was present in PM21 over the whole study period. The concentration of EC in 2004 was 56% of that in 1994. The ratio of EC21 to PM21 showed a decreasing trend fmm 1998 onwani that coincided with the introduction of long-term regulation of diesel vehicles. SO42-, NO3-, and Cl- concentrations showed seasonal variation. NO3- and Cl- were negatively correlated with ambient temperature. It was difficult to evaluate the both ionic components of collected sample on the filtec because the both ionic components were lost fmm the sample by volatilization. Thus, we have re-evaluated the animal trend using the data observed during cold periods (<16°C). Yearly average Cl- concentration in cold periods showed a decreasing trend. This trend was probably the result of a reduction in Cl- emissions in response to the regulation of incineration furnaces as part of dioxin-control measures. We concluded that the decreasing trend in the levels of these various emissions in the Tokyo metropolitan area was the result of the enforcement of emission regulations.
