BEIJING -- Air quality in Chinese cities has continued to improve in the first four months of the year, according to the Ministry of Ecology and Environment.

For 339 cities monitored by the ministry, the proportion of days with good air quality came in at 85.1 percent in the January-April period, up 1.3 percentage points from the same period last year.

The average density of PM2.5, a key indicator of air pollution, dropped 4.9 percent year on year to 39 micrograms per cubic meter while the average PM10 density declined 8.7 percent from a year ago to 63 micrograms per cubic meter, data from the ministry showed.

The Beijing-Tianjin-Hebei region and the neighboring areas reported 68.1 percent of days with good air quality from January to April, up 4.9 percentage points from a year ago.

Beijing, in particular, reported good air quality on 86.7 percent of the days during the period, jumping by 20 percentage points year on year. The city's PM2.5 density declined 32.1 percent year on year to 36 micrograms per cubic meter.