What caused the severe smog in Northeast China?

Causes of smog: inversion, automobile exhaust, burning straw.

What is the reason for the large-scale fog in Northeast China? According to the Environmental Protection Department of Heilongjiang Province, the emission of pollutants from coal combustion in Harbin is relatively large, the exhaust pollution from motor vehicles is serious, straw burning is repeatedly prohibited in autumn, the prevention and control measures for dust pollution are not perfect, the inversion phenomenon is serious since the weather turned cold, and the diffusion of air pollutants is difficult. Changchun Environmental Protection Bureau also said that the five-day inversion and too small wind were the main reasons for the foggy weather. "The recent smog weather in Changchun has nothing to do with air pollution in North China."