An aircraft flies amid heavy smog over the suburb of Beijing, China, January 2, 2017.
Over the new year holiday, hundreds of flights were canceled and highways closed across northern China as average concentrations of small breathable particles known as PM2.5 soared above 500 micrograms per cubic meter in Beijing and surrounding regions.Pollution alerts are common in northern China, especially during bitterly cold winters when energy demand, much of it met by coal, soars.
But the Beijing Municipal Environmental Protection Bureau told state media that PM2.5 concentrations dropped 9.9 percent on the year to an average of 73 micrograms per cubic meter in the Chinese capital in 2016.
The total number of "blue sky days" reached 198 in 2016, up 12 from the previous year. However, the average PM2.5 measure still exceeded national air quality standards by 109 percent, the bureau said.
Despite a brief respite on Monday, smog returned to the Chinese capital on Tuesday, with PM2.5 readings again at "hazardous" levels. The city environment bureau said the orange alert was expected to last until Wednesday.
China is in the third year of a "war on pollution" aimed at reversing the damage done to its skies, soil and water after decades of untrammeled economic growth.
It has created emergency response systems that restrict traffic and shut down factories and construction sites during periods of heavy smog, and it has also vowed to punish local officials and enterprises that break rules.
During a bout of smog in December, inspectors identified 21 enterprises that had violated regulations by failing to close operations on time, and 10 more inspection teams were dispatched to cities across the region over the new year.
But government officials have expressed frustration that persistently heavy winter pollution, brought about by unfavorable weather and the use of coal-fired urban heating systems, has overshadowed the genuine progress China has made to reduce smog.