Pollution levels in Beijing over the past six months were the lowest in nearly a decade, environmental officials said yesterday.

"We can say air quality in Beijing has already improved. We can feel that and see blue skies here," said Du Shaozhong, vice director of the Beijing Environmental Protection Bureau.

Part of the improvement has been due to the continuation of some measures imposed during the Olympics last year, said Du.

Beijing recorded 146 days this year that fell within the country's national standard for acceptable air, he said. When the air pollution index (API), which measures four major pollutants, is under 100, China considers it a "blue sky day."

So far this year, Beijing saw 23 more "blue sky days" than during the same period last year, the environmental bureau said. Meanwhile, the average pollution readings for January, March, April, May and June were the best since 2000.

However, the air in February was worse than last year and included one particularly smoggy day, February 10, when the API hit 307. China labels such levels "heavy pollution" and encourages people to stay inside.

The capital's polluted air underwent a massive cleanup campaign for last summer's Olympic Games.

City officials planted thousands of acres of trees in and around the city, shut down scores of factories, stopped almost all construction and removed 2 million vehicles from the roads for a two-month period.

A limited version of traffic restrictions continued after the games.

The pollution index readings have shown drops in several key pollutants, including Beijing's worst one -- dust particles known as PM 10.

However, Beijing does not currently measure ozone or finer particulate concentrations known as PM 2.5, considered most dangerous to human health.

Yu Jianhua, director of the Beijing Municipal Monitoring Center, said national standards had not been set for those pollutants.