In FY 2002, which is the year with the highest frequency of Asian dust days identified in meteorological observatories in Japan, the attainment of air quality standards (AQS) for suspended particulate matter (SPM) was poor compared with attainment of AQS in recent years. We examined an interannual variation of the attainment of AQS and considered the effects of Asian dust episodes tothe attainment of AQS for the period FY 1992-2004. The yearly attainment of AQS satisfies the following two standards:(1) 98-percentile value of the daily mean concentration is below the threshold (100μgm-3), (2) high concentration exceeding the threshold never continues on subsequent days. A remarkable Asian dust episode was widely observed in April 2002. The SPM concentration during the dust period was not so high (100-200μgm-3) but the dust persisted for the 8-11 April period. As a result, this episode showed a reduction of approximately 40% in the attainment of AQS in FY 2002. By contrast, another dust episode, 21-22 March 2002, brought an extremely high concentration (>500 μgm-3 in the highest polluted sites). The period of high concentration lasted about 30 hours. Therefore, the attainment/non-attainment area in FY 2001 depend on the beginning and end of the dust period whether it spreads over a border time (00 JST) for calculating daily mean values. The number of high concentration days in a year is smaller in recent years than that in 1990s, particularly in late autumn and early winter. Owing to the reduction of high concentration days in a year, the low-level attainment of AQS in FY 2002 is substantially caused by the single dust episode observed during the 8-11 April period.