Just how much are people willing to pay for clean air?

By analyzing census data and purchases of air purifiers in 81 cities, researchers found an answer to that question in China, at least.

On average, Chinese households are willing to pay $5.46 to remove one microgram per cubic meter of pollution from their home. Findings are published in the National Bureau of Economic Research.

Results varied widely between the poor and rich on how much they were willing to pay to reduce pollution. People with high incomes were willing to pay as much s $15 per microgram.

“We found that average Chinese households substantially value clean air, but also that how much they value it depends greatly on how much money they earn,” said study author Koichiro Ito, of the University of Chicago. “Understanding these factors can help regulators decide which reforms and regulations would be most effective.”

Reforms are badly needed; air pollution causes about 6.5 million deaths per year, largely due to pollution from coal plants. And there are a lot of coal plants in China: A report released this week by Greenpeace found that China is adding an average of one new coal-fired plant a week. While air purifiers may help to some extent indoors, they are only accessible for those willing — and able — to pay.