Chinese factories, coal plants, and millions of new cars are an obvious source of Beijing’s thick smog. But they also contribute to air pollution in California.
New research at the University of California-Davis finds that in the state’s Central Valley–one of the most polluted places in the country, with asthma rates twice as high as the rest of California–around 10% of ozone pollution is coming from outside the state, and mostly from Asia.
Secondhand smog is sucked in through the gap of the Golden Gate Bridge, through the Bay Area, and then ends up settling down in the Central Valley. By taking samples of air particles on a mountaintop near the coast, and in the valley, researchers were able to separate out individual particles and figure out where they came from.
“We have a lot of information to talk about the composition of these particles in different sizes,” says UC Davis atmospheric scientist Ian Faloona. “We put that into a big statistical washing machine, basically, and it shakes out groupings of what are the most common sort of combinations of these aerosol types that we see.”
Particles from Asia are recognizable because of their unique blend of elements–like aluminum or iron–from local soil. “Certain soils from certain types of the planet have different ratios of these elements,” says Faloona. “So we look at a whole host of these ratios and we see that this looks like the majority of these crustal elements are coming from Asian dust. That’s kind of how we fingerprint it.”
The method can’t identify that pollution is coming from a particular country, because the smog tends to be blown in from continent-wide storms that sweep across Asia. Still, the researchers say that much of it is probably coming from China.
“In what we know of emissions in Asia, the signal is swamped by China,” says Faloona. “China is so large and industrializing so rapidly that the bulk of those emissions are definitely attributable to China.”
International pollution can also be tracked by computer models that look at emission sources and weather patterns, and as the models improve, it will eventually be easier to pinpoint the source of pollution in smaller areas. That may lead to lawsuits–in North America, there have already been international lawsuits where the U.S. blamed Mexico for pollution, and Canada blamed the U.S. for emissions causing acid rain.
As agencies like the EPA better understand where pollution is coming from, it may also help shape better local policy–so cities and counties are responsible for reducing only the pollution that’s actually under local control.
Faloona hopes that the research changes how people think about the problem of smog. “If you think about it, the way we’ve considered it, and our legal policy involving clear air, involves dicing up the atmosphere into these little bins and baskets–this is the Los Angeles basin’s problem, for example,” he says. “We used to think of it as a local or regional problem.”
Now people are realizing that, like greenhouse gas emissions, it’s a global problem.
“If you emit greenhouse gases, they stay in everyone’s atmosphere for a decade,” Faloona says. “That now all of the sudden extends the scale of your backyard to the entire planet. I think that awareness has brought to the table this idea that any solution that we address in terms of climate change has to be global in scope. Now we’re coming to realize that’s also true for air quality. We have to address this globally.”