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GUANGZHOU, Jan. 3 -- The Pearl River Delta region in south China's Guangdong Province has seen improving air quality in the past few years, local authorities said Sunday.

The density of PM2.5, tiny and particularly hazardous airborne particles, fell to 34 mg per cubic meter in 2015 from 58 mg per cubic meter in 2007, according to the provincial environmental protection bureau.

The level nears the healthy maximum of 35 mg per cubic meter set by the Chinese government.

The delta region, a manufacturing center, includes nine cities such as Guangzhou, Shenzhen, Dongguan, Foshan and Zhongshan. It is in sharp contrast to many northern regions suffering severe smog.

Despite declines in PM2.5 levels, the region faces rising ozone pollution, especially in cities of Guangzhou, Foshan, Dongguan and Zhaoqing, said Zhong Liuju, the bureau's chief air expert.

In the past few years, the authorities have set safe emission standards for volatile organic compounds in industries like plating, printing and furniture to combat ozone pollution, Zhong said.

The measure has helped to cut ozone pollution peaks but the average level still rises by 0.8 mg per cubic meter a year, he said.