In the northern city of Harbin, China, air quality was so bad ten days ago that concentrations of particulate matter reportedly reached 1000 micrograms per cubic meter at their peak, exceeding the World Health Organization's daily safe levels by a factor of 40 and shrouding the city in a fog so dense that commuters had trouble finding their way and a numbers of schools were forced to close. As China's pollution has reached intolerable levels,...

