More than 80 percent of cities failed to meet the national air quality standard during at least half of December, making it the month with the worst average air quality in 2013, according to information released by the Environmental Protection Ministry on Friday.

Out of the 74 cities officially monitored, 62 failed to reach the standard on 15 days out of the month, which was twice as many as the number in November.

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Only three cities reported good air quality on more than 24 days in December: Lhasa, in the Tibet autonomous region; Kunming, in Yunnan province; and Zhangjiakou in Hebei province. In November, that total was 12 cities.

The poor air quality in December stemmed from the smog that enveloped 104 cities in 20 provinces across China in early December, reducing visibility to less than 10 meters in some places.

“Whether we can take effective action to ease the pollution during smoggy days will have a big impact on the improvement of total air quality,“ said Chai Fahe, vice-president of the Chinese Research Academy of Environmental Sciences.

Levels of five major air pollutants grew in December. The monthly average of PM2.5 — particulate matter smaller than 2.5 microns in diameter, which can enter deep in the lungs — increased by almost 56 percent.

Compared with November, the number of days with good air quality in the 13 cities o

f the Beijing-Tianjin-Hebei province cluster in December dropped by about 5 percentage points, a relatively small decline in contrast with the Yangtze River Delta region and the Pearl River Delta region.

Almost all of the 34 monitored cities from those two regions failed to report good air quality during more than 15 days in December.

The number of days with good air quality in the Yangtze River Delta region fell by more than 24 percentage points from November. For the Pearl River Delta region, the decrease was more than 45 percentage points.

Hebei province ranked sixth on the list of top 10 most polluted cities issued by the ministry. In fact, it was on the list every month in 2013.

Nanjing and Huai'an, two cities from Jiangsu province, made it onto the list for the first time.

Beijing will begin issuing official guidance to inform the public if the weather is conducive to setting off fireworks and firecrackers during the upcoming Spring Festival, according to an announcement from the Beijing Meteorological Bureau on Friday.

The updated guidance includes four levels of advisability regarding the use of fireworks, as opposed to the three issued in 2013, which were: proper, not quite proper and not proper.

The newly added level is a harsher one: “extremely improper“.

The local governments of Beijing, Tianjin and Hebei province will also issue the guidances using more channels than in the past, including text messages and on websites.