Beijingers spent nearly half of 2015 breathing air that did not meet national standards, Chinese media reported Tuesday, as the city struggles to address a smog problem that has provoked widespread public anger.

The Chinese capital faced 179 polluted days last year, with 46 of them considered heavily polluted, according to the Global Times, citing figures from the city's environmental protection bureau.

Levels of PM2.5 -- harmful microscopic particles that penetrate deep into the lungs -- averaged 80.6 micrograms per cubic metre over the year, the newspaper said, more than eight times the World Health Organization's recommended maximum annual average exposure of 10.

The figures represented a 6.2 percent decrease year-on-year, but still left citizens breathing air that was 1.3 times the country's own standard, which is not as strict as the WHO's.

After a comparatively mild year for pollution, Beijing in December declared its first ever red alert for smog, the highest level of a four-tier system, prompting authorities to order thousands of factories to close or curb their activities and pull half of all private cars off the streets, among other measures.

The decision came in response to public anger after the city failed to put the system, established in 2013, into action after heavy smog hit the city earlier the same month.

The move set off a domino effect, with cities across China's polluted east and north declaring their own alerts, with PM2.5 levels climbing to over 700 in some areas. The entire eastern province of Shandong, home to almost 96 million people, issued its first ever alert.

Beijing followed up with a second alert later in December, but then ignored successive waves of smog that struck the city around Christmas.