Sales of PM2.5 detectors are booming in China following frequent rounds of smog in northern parts of the country.

Seeking better protection from the lung-choking smog that plagues Beijing, Wang Hongtao, a technician in his 40s, recently made an online purchase of a PM2.5 detector for more than 900 yuan ($130).

Wang said: "As smog gathers again and again in Beijing, I'm really concerned about health problems. With the PM2.5 detector, I can find out the condition of indoor air quality. Once the PM2.5 levels exceed 50 or 60, I will immediately open the air purifiers.