Good news: SoCal's air is better. Bad news: It's still the worst in the US

Southern California once again ranks among the worst for air pollution in the annual “State of the Air” report from the American Lung Association.

Over a period from 2010 to 2012, the Los Angeles metropolitan region, including Long Beach and Riverside, ranked No. 1 in America for ozone pollution and ranked in the top five in terms of particle pollution, despite consistently improving air quality over the past several decades.

“Our report shows that California is making real and steady progress in the fight for clean air but we still have significant challenges ahead,” said Bonnie Holmes-Gen, Senior Director of Policy and Advocacy for the American Lung Association in California. “Unhealthy levels of air pollution are putting the health of millions of Californians at risk.”

Ozone is a gas produced when chemicals from things like car emissions and industrial processes are exposed to sunlight and high temperatures. It can irritate and even burn lung tissue and inhibit respiratory function.

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Particle pollution, a mixture of soot and gas with particles smaller than 2.5 microns, can cause many adverse health effects. When it’s breathed, it can pass through the lungs and into the bloodstream, leading to possible heart attacks, strokes or lung cancer and exacerbating conditions like asthma and allergies.

“That pollution that we see in Los Angeles isn’t just an annoying haze but a real public health danger,” Holmes-Gen said.

The Los Angeles basin is unfortunately uniquely suited to ozone pollution, said Prof. Suzanne Paulson, director of the UCLA Center for Clean Air.

The high density of transportation, with cars, diesel trucks, air traffic and shipping  produces volatile organic compounds and oxides of nitrogen – the chemicals that can turn into ozone. Sea breezes push them over the basin and the abundant sunlight transforms them into ozone, which is then trapped by the mountains to the east.

“It’s a combination of the ring of mountains and wind direction and lots of sources upwind that produces the high ozone,” said Paulsen.

Particle pollution is caused by many of the same transportation sources, particularly heavy diesel trucks, or the burning of wood and other materials in chimneys or wildfires.

Despite the dire-sounding ranking, Holmes-Gen stressed that the big picture for air quality in Southern California is positive. Over the fifteen years the American Lung Association has compiled the annual report, the number of dirty air days in Los Angeles has dropped by 38 percent.

However Holmes-Gen cautioned that during the current report period, hotter weather conditions resulted in a slight uptick in the ozone pollution days in Los Angeles compared to the previous two years.

“We have to be very aware that warming temperatures and climate change can slow California’s progress,” she said.

Paulsen pointed out that many of the measures being taken to mitigate climate change, like reducing carbon emissions and moving away from combustion engines to more electric vehicles, will also cut air pollution.

“There’s a lot of potential for win-win solutions to both climate and air pollution.”