BEIJING - Density of key air pollutants PM2.5 and PM10 shot up in China by 46.2 percent and 39.6 percent respectively in October, the environmental watchdog announced on Tuesday.

The Ministry of Environmental Protection attributed the rise to seasonal change.

Nearly half of the 74 ?major Chinese cities monitored nationwide had more than 50 percent of the days in October failing to meet ministry standards.

Air quality in south China's Pearl River Delta reported marked drop compared with September mainly because of less rain and more sunshine. The density of PM2.5 and PM10 increased 89.5 percent and 73.8 percent.

The nine monitored cities in Pearl River Delta averaged about 24 days below the standard, while the national average stood at around 15 days.

The ten cities with the most serious problem last month are Shijiazhuang, Xingtai, Baoding, Handan, Tangshan, Jinan, Harbin, Hengshui, Xi'an and Wuhan.

China faces severe air pollution challenges. Heavy air pollution haunted Harbin, capital of northeast China's Heilongjiang Province, from October 19 to 23, disrupting transport and forcing closure of schools.

In September, a government plan to tackle air pollution by cutting coal consumption, shutting down polluters and promote cleaner production was announced. The plan also aims to cut density of inhalable particulate matter by at least 10 percent in major cities nationwide by 2017.X ? China has 668 air quality observation points in 114 cities, including ?172 newly added points in 40 medium-sized cities which went live in October.