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) NO
2 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 NO
2 concentration increased appreciably. In addition, NO
2-pollution extended to the cities whose population is less than 500, 000.
(3) NO
2 concentration increased in particular in the cities that located in industrial areas and in the vicinity of express highways.
View full abstract