Why is air quality bad in Los Angeles today?

LOS ANGELES - An Air Quality Alert was issued by the South Coast Air Quality Management District for Los Angeles and surrounding areas, in addition to a mandatory wood-burning ban effective through midnight Friday due to high air pollution.

The residential wood-burning ban was originally expected to expire Thursday night, but it will now be in effect until at least 11:59 p.m. Friday for areas including the non-desert portions of Los Angeles, Riverside and San Bernardino counties, and all of Orange County, according to the National Weather Service.

Residents in the affected areas are reminded that burning wood in their fireplaces or any indoor or outdoor wood-burning device is prohibited, as is burning manufactured fire logs, such as those made from wax or paper.

Mountain communities above 3,000 feet, the Coachella Valley and the high desert are exempt, according to the South Coast Air Quality Management District. Homes that rely on wood as a sole source of heat, low-income households and those without natural gas service also are exempt from the requirement.

Fine particles in wood smoke, also known as particulate matter or PM2.5, can get deep into the lungs and cause respiratory problems such as asthma.

The AQMD is urging the public to check the current and forecasted air quality levels online or via their mobile app to make informed decisions about outdoor activities.

The windy and warm conditions will also likely drive down humidity levels, possibly creating "briefly critical fire weather conditions," forecasters said. Humidity levels could fall as low as 8% by Saturday in some areas.

A cooldown is expected by Sunday.