Thousands Urged To Remain Indoors in California Over Air Quality

Air quality alerts are in place across large parts of southern California through Thursday, as a combination of wildfire smoke and ozone pollution pushes air conditions into unhealthy ranges. The National Weather Service (NWS) warns that the impacts could be serious—especially for vulnerable groups—and are urging residents to take immediate precautions to protect their health. Wildfire Smoke Triggers Widespread Air Quality Alerts File image: Smoke-filled skies over Runyon Canyon in California during wildfire season in 2025.

Air quality alerts tied to smoke from multiple active wildfires have been issued across Southern California, spanning much of the Greater Los Angeles region, including: San Fernando Valley (east and west: Burbank, Glendale, Reseda, Woodland Hills) San Gabriel Valley (Pasadena, San Gabriel, Pomona) Santa Clarita Valley (Santa Clarita, Newhall, Valencia) The San Gabriel and Santa Susana Mountains and the Highway 14 corridor The Inland Empire region, covering Riverside and San Bernardino counties Map showing areas in southern California affected by air pollution caused by wildfire smoke on Thursday, May 21, 2026 | NWS The wildfire smoke is increasing concentrations of fine particle pollution (PM2. 5). This is especially dangerous because such particles can travel deep into the lungs and enter the bloodstream.

The NWS has issued air quality alerts until Thursday evening, warning that smoke conditions can shift rapidly depending on fire behavior and wind patterns. ‘Harmful’ Levels of Ozone Pollution Drives Air Quality Alert File image: Emissions from the port of Los Angeles are seen in 2021. A separate air quality alert has been triggered by elevated ground-level ozone ( smog ), which forms when heat, sunlight, and emissions from vehicles and industry interact.

Ozone levels tend to peak in the afternoon and early evening, when sunlight-driven chemical reactions are strongest. Image showing areas in southern California affected by ozone pollution on Thursday, May 21, 2026 | NWS The area most affected by elevated ozone levels is the Imperial Valley, including the cities of El Centro, Calexico, and Brawley. The alert is in effect from late Thursday morning through to the evening, when smog concentrations are typically highest.