BEIJING -- China saw more polluted air as the average PM2.5 density, a key indicator of air pollution, climbed 6.2 percent year-on-year to 34 micrograms per cubic meter in the first six months, official data showed.

For 339 cities monitored by the Ministry of Ecology and Environment, the share of days with good air quality stood at 81.4 percent during the period, down 3.2 percentage points, year-on-year.

The average density of PM10 went up 10.9 percent from a year earlier to 61 micrograms per cubic meter, data from the ministry showed.

A key region for air quality improvement, the Beijing-Tianjin-Hebei region, along with the neighboring areas, saw its share of good air quality days edge down 3.5 percentage points to 57.5 percent in the first half of the year.