An American graduate from Princeton started an online shop on taobao.com to sell homemade air filter kits, making, beyond his expectation, as much as 500,000 yuan ($81,784) per day during some of the most polluted days in Beijing.

Gus Tate, now living in a hutong near Yonghe Lama Temple in Beijing, launched Smart Air Filters last year when the haze hit Beijing and his friend Thomas Talhelm made a cheap and effective air filter by strapping a high-efficiency particulate absorption (HEPA) filter onto a fan.

Later, they launched a website and opened a Taobao shop, which accept orders for homemade air filters at a minimum price of 200 yuan ($33), much lower than the current market price of household air filters costing thousands of yuan.

"The revenue reached average 10,000 to 15,000 yuan per day last week. Sales volume fluctuates according to the weather. People are willing to spend money on health when there's severe smog. Sales are expected to surge recently," said Gus Tate as persistent smog shrouded Beijing last week, uschinapress.com reported on Sunday.

Tate's homemade air filters have become a hit in Beijing and in other big cities, such as Shanghai, Hong Kong and Guangzhou.

"I bought an air filter from Tate's online shop in June, due to its low price and air-purifying result claimed in its advertisement," said Wu Yan, a 26 year-old woman in Beijing, "It seems to have some effect, but I stopped using it because it makes noise."

The increasingly frequent air pollution in China has spurred a revival of related industries. Air-quality testers, food that benefits lungs, air-purifying plants and tourism programs are just some of the products in a long list of anti-smog items that are selling like hot cakes.

3M face mask, a US brand that is especially effective for smoggy days, has also become popular in the e-commerce market. By the end of October, there were 2,247 shops selling 3M face masks on taobao.com, one of the largest China's online shopping platforms.