TAIPEI, Jan. 7 (Xinhua) -- The city of Tainan in southern Taiwan had the worst annual reading of PM10, a major air pollutant, among all cities and counties in Taiwan in 2019, a local environmental group said Tuesday.

The annual average density of PM10, particulate matters measuring up to 10 micrometers in diameter, in Tainan reached 48.35 micrograms per cubic meter (mcg/m3) in 2019, followed by neighboring Chiayi County with a reading of 48.27 mcg/m3, said Yeh Guang-perng, founder of Air Clean Taiwan, at a press conference in Taipei.

Taitung County in eastern Taiwan had the best reading of 20.5 mcg/m3.

In terms of regions, Hualien and Taitung in eastern Taiwan had the least PM10 pollution with a reading of 21.1 mcg/m3 while the region of Yulin, Chiayi and Tainan in the south had the worst with a reading of 47.2 mcg/m3.

The island's southern region has suffered worse air quality and the gap between the southern and northern regions has been expanding over the years, Yeh said.

Taiwan's PM10 limits -- a 24-hour average of 125 mcg/m3 and an annual average of 65 mcg/m3 -- have not been revised since 1999.

Air Clean Taiwan has repeatedly urged the authorities to revise the outdated standards and adopt those of the WHO, a 24-hour average of 50 mcg/m3 and an annual average of 20 mcg/m3, Yeh said.

This marks the ninth year that Air Clean Taiwan has published annual readings of PM10 across the island.