In Beijing, the levels of pollutants harmful to human health rose sharply, says government official.
The head of the Beijing Municipal Environmental Protection Bureau, Chen Tian, Wednesday said nitrous dioxide and large particulates known as PM 10 climbed by 30 percent in the first three months of the year.
Another of the most frequently detected pollutants was sulphur dioxide, although its level in the atmosphere was down slightly in the January-March period.
Separately, the Xinhua news agency cited the China Meteorological Administration as saying pollution levels last month were the highest for a month of March in 52 years.
"There were no strong winds to disperse the pollution cloud," CMA representative Chen Zhenlin said.
Since the beginning of this year, dangerously high concentrations of air pollutants have lingered over large areas of China for more than three days and, in some cases, for more than 15 days.
Beijing was especially hard hit, registering severe air pollution on 26 out of 31 days in January.
On its worst day, the Chinese capital had an extremely high level of small particulates - known as PM 2.5 - of 993 micrograms per cubic meter of air.
Those particulates are especially dangerous because they can penetrate people's lungs and enter the blood stream.
Under China's own standards, a PM 2.5 level above 200 micrograms per cubic meter is considered harmful to people with lung or heart disease, while the World Health Organization says a level of 25 micrograms per cubic meter or higher is a threat to public health.
The world's second-largest economy has neglected the environment for decades in its quest for rapid industrial development, a growth strategy that has resulted in severely polluted air, rivers and lakes.