Reading the index shown by the air quality forecast application on her mobile phone has become a daily routine for Yang. She is cutting down on her jogging outside as well the time her children spend outdoors.

To maintain the air quality at home at a healthy level, Yang spent 7,000 yuan on two air purifiers, which now run 24 hours a day. "I feel obliged to make my 3-year-old daughter stay at home for most of her leisure time," she said.

The frequency of smoggy days has been widespread from the major northern cities to southern and western regions in China since the beginning of winter.

The Ministry of Environmental Protection said earlier that there were three major reasons behind the widespread haze: unfavorable weather conditions making it difficult for pollutants to diffuse, motor vehicle exhaust, and coal consumption for winter heating.

Official data showed that 2013 had the most smoggy days in the past 52 years. Since the beginning of December, at least 25 regions and provinces have reported high pollution levels, particularly of PM2.5, which are tiny floating particles measuring 2.5 micrometers or less in diameter. PM2.5 particles are especially hazardous because they can settle in the lungs and cause illnesses such as respiratory problems.