Continuous measurements of NO_x(NO + NO₂) , O₃ and wind speeds and directions were carried out from 1987 to 1994 on both sides of Route 1 in Okazaki City, Aichi, Japan. The concentrations of NO_x and O₃ were measured every hour, and the wind speeds and directions were recorded every minute. Vertical distributions of NO_x concentration were observed in three levels for 5 days in January, 1994. The NO_x behavior on both sides of Route 1 was suggested as follows:

1. The back ground component of NO₂ is 50-80%, the oxidized component is 10-40%, the exhausted component from vehicles is 10-20%.
2. The oxidized component of NO₂ is caused by O₃ photochemical oxidations which is thought to be a rare case in winter.
3. The mixing height due to vehicles is thought to be 9-14 m on the basis of NO_x vertical distributions.

The photochemical oxidation of NO should be considered to solve a problem of high-level NO₂ on the roadside .