BEIJING — Fog has joined smog in the Beijing skies barely a month before the Olympics and as a cleanup of the algae-choked sailing venue in the eastern city of Qingdao continues.

Beijing has been shrouded in mist for 12 days, reinforcing the image of a city choking in fumes. In fact, the drizzle has helped clear the atmosphere of dust and reduced pollution over the past week, Beijing’s environment bureau said yesterday.

The capital has recorded six straight days of air quality in the “good” category on Beijing’s scale, with the index falling to 69 in the 24 hours to noon yesterday. The World Heath Organization recommends a maximum reading of 50, while Beijing rates 100 as “good.”

“The good air quality recorded is proof that the city’s drive to clean up pollution is showing results,” the Beijing Municipal Environment Protection Bureau said in a statement on its Web site.

Beijing is closing factories, halting construction, and taking about half the cars off its roads in an effort to reduce pollution in time for the August 8-24 games. The International Olympic Committee has said it may reschedule some events if athletes are at risk.