With its sprawl of tract homes, apartment complexes, shopping centers and warehouses, Ontario looks like many other communities in the Inland Empire and shares the same environmental woes, including heavy truck traffic and air pollution.
But people in one neighborhood near the 60 Freeway have a dubious new distinction: They are breathing the dirtiest air in Southern California, according to new measurements by pollution regulators.
A new air monitoring site near the busy traffic corridor had the highest concentrations of lung-damaging soot in the region, surpassing federal health limits and the readings in Mira Loma in Riverside County. Mira Loma's levels of soot, also known as fine-particle pollution, had been regarded as Southern California's worst.
The readings were taken by the South Coast Air Quality Management District as part of its first continuous measurements of soot and other exhaust pollutants near freeways. The measurements provide compelling new evidence that local traffic pollution is adding to regional smog and threatening the health of more than 1 million Southern Californians who live within a few hundred feet of a freeway.
Health experts have known for years that people living near major roads breathe higher levels of air pollution and face greater risk of asthma, heart disease, lung deficiencies and a variety of other ailments. But air quality officials did not regularly measure pollution near freeways until new federal requirements kicked in last year.
Joe Ponce, who lives about two blocks from the new air quality monitor near the 60, said he sees evidence of air pollution in the fine black dust that settles on his Ontario home's roof and the increasing number of cars and trucks blasting by on the freeway.
"Anybody who lives next to a freeway is going to tell you that there's more trucks than ever before," he said. "When we were going through the recession, you could count them on one hand. Now they're a solid lane."
His neighbor, Rick Santos, was surprised and frustrated to learn of elevated pollution levels in the neighborhood of tile-roof, ranch-style houses.
"What can we do about it?" he said. "We can't reroute the freeway. We can't cut down on the traffic. We're stuck between a rock and a hard place."
The average concentration of fine-particle pollution at the monitoring site about 30 feet from the 60 Freeway, was 18.7 micrograms per cubic meter from January to March. The air district released preliminary results in response to questions from The Times about what the first permanent monitoring stations near Southern California freeways were detecting.
Federal health standards limit annual concentrations of fine-particle pollution, also called PM2.5, to 12 micrograms per cubic meter. Mira Loma averaged 17.9 micrograms per cubic meter over the three-month period, air district officials said.
Environmentalists say the findings show that regulators are not doing enough to cut pollution and reduce health risks, especially in inland communities that are crisscrossed by freeways and other traffic corridors frequently used by trucks.
"It's not just people living along the 60 Freeway — anyone close to that many diesel trucks is going to be breathing the same heavy pollution," said Penny Newman, who heads the Riverside County-based Center for Community Action and Environmental Justice.
For decades, air quality officials deliberately measured pollution at a distance from traffic and other big pollution sources. But U.S. Environmental Protection Agency requirements that took effect last year require more than 100 big cities to place pollution monitors next to major roads and use them to determine whether the air meets health standards.
The regional AQMD, which regulates pollution in Los Angeles, Orange, Riverside and San Bernardino counties, has installed four new air quality monitors next to freeways, but has made little of the data public. The other sites are next to the 5 Freeway in Anaheim, the 10 Freeway in Ontario and the 710 Freeway in Long Beach.
Air quality regulators believe soot pollution was worst near the freeway in Ontario because of the combined effect of higher smog in the Inland Empire and traffic emissions, which boost PM2.5 levels by about 10%.
Philip Fine, the air district's deputy executive officer, said the readings could be skewed because they were taken in winter, when fine-particle pollution is higher. The readings could change once a year's worth of measurements are completed.
About 215,000 vehicles a day passed by the new Ontario monitoring station in 2013, more than 25,000 of them trucks, according to the most recent data available from the California Department of Transportation.
The new stations have also detected higher levels of exhaust gases. Levels of nitrogen dioxide near the freeway are on average about 60% higher than in the region as a whole, while carbon monoxide levels are about twice as high, AQMD officials said. But neither of those pollutants are elevated enough near the freeway to violate health standards.
Most concerning of the pollutants being measured are fine particles, which are released by diesel engines, fires, power plants and other combustion sources and measure less than 1/30th the width of a human hair. Their tiny size allows them to be inhaled deep into the lungs, where they can impair breathing and damage the heart and blood vessels. Health studies link chronic exposure to fine particles to thousands of premature deaths a year in California, primarily from heart attacks and cardiovascular disease.
The elevated readings near the freeway could pose an additional obstacles for the region's air quality regulators, who have struggled to make progress cleaning fine-particle pollution.
Earlier this year, the AQMD announced it would miss a 2015 deadline to meet a key federal health standard for soot.
AQMD officials blame the California drought for reversing a long-term decline in fine-particle pollution. They say fewer storms and rainy days have allowed pollution to build up, boosting the number of bad air days over two consecutive winters. The air district has asked the U.S. Environmental Protection Agency to downgrade the region's fine-particle pollution status to "serious" from "moderate."
The change in status will give the region four more years to meet the EPA's health standard but may trigger more stringent emissions rules for some of the region's largest facilities. Air quality officials say they will be unable to achieve that standard without more aggressive action by the federal government to curb pollution from heavy-duty trucks, trains and airplanes.
California's strict vehicle emissions standards, particularly those targeting dirty diesel trucks, have already cut roadway pollution dramatically in recent years.