The riot?in Lhasa?last month not only left the city with casualties and economic losses, but also caused considerable environmental damage, with the city's air quality being the worst in its history.

"Air quality on March 14 was the worst on record since Lhasa began daily air quality reporting in 2000," Zhang Yongze, the regional environmental protection bureau director, said.

The density of sulfur dioxide was 10 micrograms per cubic meter on the day, double the city's average. The nitrogen dioxide level was 60 micrograms per cubic meter, more than double the daily average, the bureau said.

Zhang asked whether the thick smoke caused by the arson attacks on March 14 could be regarded as "concrete actions to protect Tibet's environment as trumpeted by the Dalai clique".

Lhasa is normally famed for its clean environment, but the plateau city was enveloped in dark clouds of smoke when the rioters set fire to schools, hospitals, homes and shops.

"The major factor affecting air quality here is sand dust," Zhang said.

The bureau's records showthat good air quality was recorded on 95 percent of days in 2000, and improved to 98 percent last year.

(Xinhua News Agency April 19, 2008)