The most affected cities are mainly located in the Beijing -Tianjin-Hebei region and northwest China, while pollution in the 180 cities was at prefecture level or above.
Beijing had arelatively better day today after a cold front cleared smog which enveloped the city yesterday coinciding with the opening of China's Parliament sessions.
Some legislators made a case for "smog tax" to punish the pollutingindustries.
Beijing was among the hardest hit, with an average PM2.5 density of 315 micrograms per cubic meter.
In his work report to the National People's Congress, Premier Li Keqiang said average intensity of fine particulate matter (PM2.5) dropped by 14.1 per cent in 74 cities where the new ambient air quality standards were first applied last year.