20 13. According to the inquiry of official website, Shanghai Municipal People's Government, due to the different measurement standards and evaluation methods, the years with severe smog in Shanghai are also different. Severe smog weather occurred in 20 13, 20 16, 20 17 and 2020. Among them, Shanghai's air quality index reached six levels of serious pollution at 20 13 and 12, which is generally considered to be a year of severe smog.