Multi-year trend in fine and coarse particle mass, carbon, and ions in downtown Tokyo, Japan

Long-term measurements of suspended particulate matter (SPM, <7 μm), PMfine (<2.1 μm), and PMcoarse (2.1–7 μm) were obtained from a traffic-dominated site in Tokyo, Japan for the period 1994–2004 to evaluate the effects of emission reduction measures for motor-vehicle emissions. SPM decreased from 1996 forward, with all of the downward trend attributable to the PMfine fraction. Annual average PMcoarse was constant over the 10-yr period. From 1996 to 2004, PMfine decreased at a rate of 2.37 μg m−3 yr−1 for PM2.1 mass. Most of this decrease was attributable to decreases in organic and elemental carbon. This decrease is consistent with fleet penetration of engines and fuels that complied with a stringent Japanese emission reduction limit which began to take effect in 1994. Sulfate and nitrate concentrations did not decrease over this period. Evidence of Asian dust storm contributions was found in elevated PMcoarse and water-soluble calcium levels during the spring.