Photo taken on June 11, 2015 shows a turret of the Forbidden City in Beijing, capital of China. Beijing witnessed fine weather on Thursday after days of thundershower. (Xinhua/Li Xin)

　　Beijing and its neighboring cities enjoyed better air quality in May as the main pollutants, ozone and PM2.5, both decreased year on year, according to the Ministry of Environmental Protection.

　　Ministry figures released on Monday showed that PM2.5 in 13 cities monitored in the most polluted Beijing-Tianjin-Hebei region decreased by 9.7 percent compared with the same period last year. The ozone index was down 1.1 percent.

　　Beijing reported sound air quality in 58.1 percent of the days last month and only one day of heavy pollution. Five Hebei cities featured in a list of the 10 most polluted Chinese cities in the month.

　　"The Beijing-Tianjin-Hebei region, the Yangtze River Delta region and the Pearl River Delta region all witnessed improved air quality in May compared with both the previous month and the same period last year," said Luo Yi, a senior ministry official.

　　The two delta regions refer to the economically-developed eastern and southern areas encompassing Shanghai and Guangzhou respectively.

　　China began to include an index of PM2.5, a key indicator of air pollution, and ozone in a new air quality standard at the beginning of 2013.