SHIJIAZHUANG - The smog-prone northern Chinese province of Hebei has reported fairly good air quality for 66 percent of days since Oct. 1, the best record in five years, authorities said Tuesday.

Hebei, which neighbors Beijing, is home to six of China's 10 most polluted cities, including the provincial capital Shijiazhuang, according to a Ministry of Environmental Protection report analyzing air quality in the first 10 months of this year.

Levels of PM2.5, a type of airborne particle smaller than 2.5 microns in diameter, in Hebei have fallen almost 40 percent so far compared with the same period in 2013 to an average density of 64 micrograms per cubic meter, outstripping the 25-percent smog control target set in 2013, said Wang Xiaoli, a provincial environmental protection bureau official.

Shijiazhuang has had only five days of heavy pollution since Oct. 1, down 38.6 percent year on year, and the city's hourly PM 2.5 density exceeded 300 per cubic meter only once, said Wang.

In November, periods of heavy pollution in Hebei decreased by 1,278 hours, and its hourly peak PM2.5 density plunged 38.3 percent compared with the same period last year, said Wang.

Under Chinese air quality standards, an air quality index (AQI) below 100 is defined as a good air quality day. An average daily AQI above 200 indicates heavy air pollution.

Hebei recorded the worst air quality in 2013, with only 33 percent percent of days with good air quality, according to Wang.

Overhauling polluting companies, dismantling coal-fired boilers, and controlling inferior coal have contributed to the decrease.

Winter months are known to have the worst smog in north China with Hebei hit hard as the wind slows and residents turn on coal-fired furnaces for heating.