In 1980, the Soviet meteorological service, Goskomgidromet, began collecting data on the output of atmospheric emissions classified into two broad categories: stationary sources and transport. Regionwide, stationary sources accounted for 62 percent of all air pollution in 1989, but the balance between air pollution from stationary sources and transport varied greatly by city. The Soviet meteorological service began monitoring air quality in the mid-1960s and by 1988 had checked the air for 80 substances in 534 cities. According to the Soviet environmental agency, "extensive studies" based on public health data established "a clear relationship between the level of air pollution and population morbidity." In 1988, the USSR State Committee for the Protection of Nature announced that in the cities monitored using the Indeks zagryazneniya atmosfera system, overall air quality had been improving steadily. The decrease in emissions in the Soviet Union was the result of an effort initiated by the government in the 1970s to improve urban air quality.