San Diego County is among the most polluted areas in the United States, according to a new report by the American Lung Association released Wednesday.
The 2026 State of the Air report ranked San Diego-Chula Vista-Carlsbad as the fifth-worst nationally for annual particle pollution. Last year, it landed in 59th place. The region also ranked as the seventh worst for ozone pollution.
“What we're seeing in this year's report is San Diego lands among the most polluted for both annual particles and for ozone, unhealthy ozone days,” said Will Barrett, the association’s assistant vice president for nationwide clean air policy.
Under the Clean Air Act, the U.S. Environmental Protection Agency (EPA) is required to set health-based limits for six outdoor air pollutants: particulate matter, ozone, nitrogen dioxide, sulfur dioxide, carbon monoxide and lead. The report measured fine particulate matter and ozone, which are “two of the most widespread and dangerous pollutants from this group.”
Ground-level ozone is created when pollutants emitted by vehicles, power plants and refineries react with heat and sunlight, according to the EPA, which can cause health effects even at low levels. Particle pollution, or soot, is typically caused when things are burned, such as wood or fossil fuels, Barrett said.
“They are so small they can bypass our body’s defenses and get deep into our lungs, causing all sorts of lung health concerns, including lung cancer and can cross into our bloodstream, which can affect our heart health and cause heart attacks and strokes, as well as premature death,” he added.
Barrett said new air quality monitors near ports of entry in Otay Mesa show a clearer picture of pollution in the region, which is what drove its higher ranking this year.
“What we’re seeing is the addition of new air quality monitoring data that wasn’t available in past reports,” he said. “So, now we’re getting a better picture of where some of that elevated pollution, certainly in the border region, is affecting air quality in the county.”
The air quality monitoring data comes from monitoring sites that the San Diego County Air Pollution Control District (SDAPCD) has added in recent years near ports of entry in San Ysidro and Otay Mesa.
Heavy-duty trucks and ships are the top sources of pollution in the county, he said. Annually, the Otay Mesa port of entry handles about one million northbound trucks, according to the Bureau of Transportation Statistics.
Nearby is the binational Tijuana River, a seasonal river that typically carries untreated sewage and other toxic chemicals from Tijuana year-round because of underinvestment in its wastewater treatment system.
Scientists have found that the sewage and chemicals from tires, illicit drugs and personal care products in the river become airborne. Air quality monitoring sites from the SDAPCD have shown that over the last several months, levels of hydrogen sulfide have significantly exceeded state and federal standards. People living and working near the river have reported symptoms such as headaches, nausea or respiratory issues.
Barrett said the Tijuana River sewage crisis is “really important and obviously a significant challenge that needs to be addressed,” but hydrogen sulfide was not factored into the report’s measurements.
He added that the report’s findings are “not a grade on any given county or local agency or even effort. It’s an assessment of air quality data,” but more can be done.
California, where the report found that 82% of residents live in counties with polluted air, must continue prioritizing clean air programs and implement stronger transportation-related policies, he said.
