Experts have calculated the cost of pollution in China for years, weighing the drag on productivity from medical costs, factory closures and traffic restrictions. Now economists say they know exactly how much consumers are willing to pay to clean their own air. Chinese consumers are willing to pay $5.46 on average to remove each microgram of pollutant per cubic meter of air, according a new paper by environmental economists Koichiro Ito from the University of Chicago and Shuang Zhang of the University of Colorado at Boulder. That works out to spending about $213 over five years, according to their study tracking air purifier buying habits in 81 Chinese cities over seven years. Pollution in Beijing and other large cities regularly triggers health warnings and occasionally soars to "hazardous" levels when particles smaller than 2.5 micrometers in diameter -- PM2.5 -- reach concentrations above 250 micrograms per cubic meter. The study reflects rising concern about breathing clean air as shown by more purchases of air purifiers, many of them imported, by wealthy and increasingly middle-class consumers.