The Chinese capital was on the second-highest orange smog alert in the depth of winter on Tuesday, but city officials said the air quality was improving overall, citing data from last year.

The Beijing Municipal Environmental Protection Bureau told state media the total number of "blue sky days" reached 198 last year, up 12 from 2015. It said the average PM2.5 measure — particle pollution 2.5 micrometres in size or smaller — in the city dropped 9.9 per cent to an average of 73 micrograms of particle pollution per cubic metres, but still exceeded national air quality standards by 109 per cent.

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Smog settles on central Beijing, blocking the sun even at noon. (Sasa Petricic/CBC)

Beijing also cut total coal consumption to below 10 million tonnes in 2016, down from 23 million in 2013. It closed 335 polluting factories and ordered 424,000 obsolete high-emitting vehicles off the road last year, state news agency Xinhua said.

Despite a brief respite on Monday, smog returned to the Chinese capital on Tuesday, with PM2.5 readings again at "hazardous" levels. Smog is expected to persist in the region until a cold front arrives on Jan. 8, Xinhua said.

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Workers in Beijing brave the worst stretch of smog in a year to put up Lunar New Year decorations. (Sasa Petricic/CBC)

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 untrammelled economic growth.

It has created emergency response systems to curb traffic and shut down factories and construction sites during periods of heavy smog, and has also vowed to punish local officials and enterprises that break rules.