Air pollution influences human health and the living conditions in urban area. Oxygen nitrate (NO_x) and suspended particulate matter (SPM) are emitted by vehicles. I will describe the recent air quality level for general urban areas and roadsides.

The NO_x concentration has a high correlation to the population density in Japan. It is understood that NO_x from human work contributes to air pollution. The correlation between SPM concentration and population density is law. It shows that we can not ignore the contribution of particulates from natural sources.

The NO_x concentrations at roadsides air quality monitoring stations in metropolitan Tokyo are decreasing since the 1980. However at ambient air quality monitoring stations it is not decreasing. They indicate that NO_x from vehicles is decreasing while NO_x from other sources is increasing. The SPM concentrations are decreasing since 1991 at roadside air quality monitoring stations and ambient air quality monitoring stations in metropolitan Tokyo. This indicates that the SPM is decreasing in primary emissions. It is important that we pay attention to secondary particles.

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