The National Weather Service issued an alert for parts of Southern California, warning of "harmful" levels of fine particle pollution across Los Angeles County, Orange County and the Inland Empire.
Authorities warn that particle pollution can penetrate deeply into the lungs and may lead to serious health issues, including heart attacks, bronchitis, asthma flare-ups and trouble breathing.
While anyone can be affected, the risk is higher for vulnerable groups—such as individuals with heart or lung conditions, older adults, pregnant people, children and those who spend extended time outside.
The South Coast Air Quality Management District (AQMD) also issued a particle advisory because of the potential effects of fireworks on air quality.
"Fireworks release high levels of particle pollution (PM2.5 and PM10) and air toxic metals, with July 4th and July 5th typically having among the highest particle pollution levels every year in the South Coast Air Basin," it said.
"Personal 'backyard' fireworks may lead to localized spikes in particle pollution levels and may spark wildfires, which can be a major source of particle pollution," it added.
"The smoke and combustion products from fireworks add to the particles already present in the Basin that are primarily caused by transportation and industrial emissions," the South Coast AQMD continued.
Areas affected included major cities, such as Riverside, San Bernardino, Anaheim, Irvine, Santa Monica and Long Beach.
South Coast AQMD said that on Friday, light winds combined with heightened emissions from fireworks after dusk were expected to raise pollution levels in the South Coast Air Basin. As a result, the Air Quality Index (AQI) could at times reach the hazardous range in much of Los Angeles and Orange counties as well as the Inland Empire.
On Saturday, according to South Coast AQMD, particle pollution levels are expected to stay elevated into the morning, then decline during the day as winds help disperse the pollutants. The AQI may again occasionally reach the hazardous range, with inland areas likely experiencing these high levels for a longer duration than coastal regions.
Residents in affected areas are advised to take steps to help keep indoor air clean when the outdoor air quality is poor—including keeping windows and doors closed and avoiding other sources of pollution, such as fireplaces, candles, incense, grilling and gasoline-powered lawn and garden equipment.
The AQI measures air pollution on a scale from 0 to 301 and above.
0–50: Good. Air quality is satisfactory.
51–100: Moderate. Air quality is acceptable, with potential concerns for sensitive individuals.
101–150: Unhealthy for Sensitive Groups. Air quality may affect people with heart or lung disease, older adults, children and pregnant individuals.
151–200: Unhealthy. Everyone may begin to experience health effects, and sensitive groups may see more serious effects.
201–300: Very Unhealthy. The risk of health effects is increased for everyone.
301 and above: Hazardous. The air quality requires a health warning of emergency conditions, and everyone is more likely to be affected.
What People Are Saying
Jonathan Grigg, a professor of pediatric respiratory and environmental medicine at Queen Mary, University of London, previously told Newsweek that there are "very clear links" between inhaling particles and earlier death from both respiratory and cardiovascular diseases.
He added: "There are vulnerable groups and classically they are children because they've got an extra issue to do with their lungs developing, whereas our lungs are not developing as adults."
The South Coast Air Quality Management District wrote on X on Thursday: "#FIREWORKS PARTICLE POLLUTION ADVISORY (July 4-5): Poor air quality due to #IndependenceDay fireworks is likely this #FourthofJuly holiday. Personal 'backyard' fireworks also contribute to this air pollution and may lead to negative health effects."
The National Weather Service said the air quality alerts were in effect from 5 p.m. on July 4 to 11:59 p.m. on July 5.
