BEIJING, Sept. 19 (Xinhua) -- Chinese cities had "good" air quality on nearly 90 percent of days in August, a slight year-on-year drop, but the level of key pollutants PM2.5 and PM10 has declined significantly, official data showed Tuesday.

The 338 cities monitored by the Ministry of Environmental Protection (MEP) reported good or excellent air quality on 89.3 percent of August days, down 0.9 percentage points from August 2016, according to Liu Zhiquan, head of environmental monitoring at the MEP.

During the same period, the density of PM2.5 nationwide dropped 14.3 percent from a year ago, and the density of PM10 9.6 percent.

Beijing had more "good air" days last month as PM2.5 density fell 19.1 percent year on year.

However, air quality worsened in the Beijing-Tianjin-Hebei area. PM2.5 in 13 cities rose 5.4 percent in August, while PM10 increased 9.5 percent.

To improve air quality in the upcoming autumn and winter, the MEP began a new round of on-site environmental inspections earlier this month in cities around the Beijing-Tianjin-Hebei region.

The government has encouraged use of cleaner fuel for heating in north China, where coal burning in winter is a major source of pollution.

In Beijing-Tianjin-Hebei and nearby areas, 28 cities will now use only natural gas, electricity and renewable energy for heating.