SHANGHAI — I arrived here on Oct. 19th and was greeted with this news: A combination of cold weather, lack of wind, coal-powered heating and farmers burning off post-harvest debris had created a perfect storm of pollution in the northeastern industrial city of Harbin, home to 10 million people. It was so bad that bus drivers were getting lost because the smog-enveloped roads would only permit them to see a few yards ahead. Harbin’s official website reportedly warned that “cars with headlights turned on were moving no faster than pedestrians and honking frequently as drivers struggled to see traffic lights meters away.”