After smoke from wildfires in Mendocino and Humboldt counties led to another day of unhealthy air in parts of the Bay Area on Saturday, air quality is expected to improve somewhat Sunday and in the early part of the week, according to the Bay Area Air Quality Management District.

The Spare the Air alert that was issued Saturday won’t be necessary Sunday, officials said. However, the district has issued an air quality advisory, which means that smoke could potentially affect air quality, or it could be visible in the atmosphere but won’t hurt air quality enough at lower levels where people breathe.

Forecasts on the district website show that air quality is expected to be “moderate” in most parts of the Bay Area Sunday, measuring 51 to 100 on the U.S. Air Quality Index.

When the air is “moderate,” it’s generally safe for people to open windows, go outside and move around and exercise, Dr. Stephanie Christenson, an assistant professor of pulmonology at UC San Francisco, said in an interview earlier this week. But “moderate”-rated air may bother people who are particularly sensitive to air pollution.

Air quality is expected to become “good” in some areas Monday and Tuesday, especially in Santa Clara County and along San Francisco Bay and the Pacific coast. “Good” air, measuring 0 to 50, means there is little to no risk from air pollution or wildfire smoke. But inland areas of the East Bay and the North Bay will continue to experience mostly “moderate” air quality Monday and Tuesday, according to air district forecasts.

Saturday’s Spare the Air alert was the 31st this year. It came after the Bay Area enjoyed a two-day reprieve from a record streak of 30 consecutive days of Spare the Air alerts.

Over the past month, smoke from wildfires, burning across more than 1.2 million acres throughout Northern California, has been blowing into the Bay Area and choking the region with sooty, ashy air that at times has been rated “unhealthy” or “very unhealthy.”  One day earlier this month, smoke trapped in a marine layer cast a dark orange pall over the region and kept street lamps and car headlights on through the day.

Much of the smoke lately has been generated by the August Complex fires in Mendocino and Humboldt counties, air district meteorology manager Charley Knoderer said. The August fires have burned more than 833,000 acres but were only about 31 percent contained as of Saturday evening, according to the California Department of Forestry and Fire Protection.

Knoderer said smoke from the North Complex fires, which have burned about 289,000 acres in Plumas and Butte counties, appears to be blowing mostly east over the Sierra Nevada.

Even as the air quality improves, health experts say it’s still a good idea for people to check local hourly conditions via the air district website before they open windows or go outside. District spokesman Aaron Richardson also said people can look for updated readings, sometimes at the neighborhood level, on the Fire and Smoke map from the Environmental Protection Agency.

If the air quality degrades again, no one should count on bandanas or surgical masks to protect them from wildfire smoke. Health experts said people should continue to wear them in public to prevent the transmission of COVID-19, but these masks are too loose-fitting to keep out very small smoke particles, which can also pass through cloth. Experts have also cautioned against relying on the more sought-after N95 respirator masks because they are in short supply.