Abstract
Yearly means of nitrogen dioxide concentration in 168 cities of Japan between 1985 and 1989 were statistically compared by using t-test.
The results obtained were as follows:
(1) NO2 concentration increased in 67 cities. On the other hand, no increase was recognized in 101 cities.
(2) In the cities whose population is more than 500, 000 NO2 concentration increased appreciably. In addition, NO2-pollution extended to the cities whose population is less than 500, 000.
(3) NO2 concentration increased in particular in the cities that located in industrial areas and in the vicinity of express highways.
