Air quality in the first half of 2015 in Ningbo [Provided to chinadaily.com.cn]

During the first half of 2015, the average ratio of good air quality days in Ningbo's 15 districts was 78.4 percent. And in the central urban area it was 82.3 percent, increasing 2.9 percent points over 2014, reported Ningbo municipal environmental protection bureau on July 23.

According to the report, the density of PM 2.5 (particulate matter smaller than 2.5 micrometers) in the 15 districts fell 4.1 percent over 2014. In addition, central urban area had 28 days of excellent air quality (Grade I), 121 days of good air quality (Grade II) and 32 days of Grade III or above.

The key pollutants included sulfur dioxide, PM 2.5, PM 10, ozone and carbon monoxide.

"Ningbo's air pollution features seasonality," said a department head of the bureau, adding that the density of PM 2.5 reaches a peak in winter and ozone in spring is excessive.

Comparision of air quality between 2015 and 2014 [Provided to chinadaily.com.cn]

During the first six months, the density of PM 2.5 increased gradually from southeast to northwest. In other words, it was lower in Ninghai, Xiangshan and Beilun than in Cixi and Yuyao.

"Thanks to closing down backward production facilities and optimizing industrial and energy structure, the density of PM 2.5 in the central area was relieved," the department head said.

Generally, the Air Quality Index (AQI) in Xiangshan county was the lowest, while it was highest in Jiangbei district.