2013 Northeastern China smog
A dense wave of smog began in Northeast China, especially in major cities including Harbin, Changchun and Shenyang, as well as the surrounding Heilongjiang, Jilin, and Liaoning provinces on 20 October 2013. Unseasonably warm temperatures with very little wind across northeastern China coincided with the initiation of Northeast China's coal-powered municipal heating system. Record densities of fine particulates were measured in the city. In Harbin, the levels of PM2.5 particulate matter rose to 1,000 micrograms per cubic metre, worse than Beijing's historic highs. Visibility dropped to and authorities grounded flights and closed more than 2,000 schools. In Changchun, air pollution recorded at an all-time high and the levels of PM2.5 particulate matter rose to 845 micrograms per cubic metre on 22 October 2013. The smog eased on 25 October 2013 and had completely dissipated by the 28th due to a cold front that had moved in from Russia. Background Officials blamed the dense pollution on lack of wind, burning of crop waste in farmers' fields, and 20 October start-up of Harbin's coal-powered district heating system. Harbin lies in the north of China where winter temperatures can drop to , necessitating a six-month heating season. Air pollution in Chinese cities is