Beijing saw 24 official "blue sky" days, or days with fairly good air quality, in January, which city authorities have hailed as a sign that years of anti-pollution efforts are paying off.

The number of blue sky days was two more than January last year, and a 10-year high, said the Municipal Bureau of Environmental Protection.

Meanwhile, major pollution indices, including concentrations of sulfur dioxide, carbon monoxide, nitrogen dioxide and particulate matter in the air, continued to drop markedly, said the bureau.

The number of blue sky days rose to 274 last year from 100 in 1998, when the capital launched the blue sky drive.