PASADENA, Calif., Aug. 11 (UPI) -- One of the things about gas and pollution is that they don't stay put. Sure, cities and regions that pollute the most tend to be the most polluted, but just as often, smog and smoke find their way atop less suspecting locales.
One of the unsuspecting recipients of China's excess ozone is the western United States. A new study by scientists at NASA's Jet Propulsion Laboratory suggests China's pollution is threatening to undermine the progress California and its neighbors have made in reducing ozone levels over the last decade.
Ozone, or O3, is one of the most abrasive components of smog, the long-hanging pollution that occasionally forces Los Angeles residents to stay indoors.
Ozone itself is not directly emitted; it's a secondary pollutant, the byproduct of chemical reactions in the lower atmosphere involving manmade pollutants like nitrogen oxides, carbon monoxide and other volatile organic compounds. Once formed, ozone hangs around in the atmosphere for several weeks. It can have a greenhouse gas effect, boosting temperatures, as well as causing respiratory and other health problems.
According to the latest analysis, between 2005 and 2010, western states cut ozone-forming pollutant levels in the lowest layer of the atmosphere, the troposphere, by more than 20 percent. But ozone levels in the midtroposphere, the layer of atmosphere spanning 10,000 to 30,000 feet above sea level, has stayed put -- no progress.
One of the reasons, researchers say, is the influx of ozone and ozone-forming pollutants being transported by atmospheric winds across the Pacific.
"The contribution from China increased steadily throughout the study, and we don't know what will happen to it in the future because it depends on human rather than natural factors," JPL scientist Jessica Neu, a co-author of the paper, explained in a press release.
China isn't simply a perpetrator. It's a victim, too. Pollution from India routinely blows into its southern valleys. Transnational pollution is a global problem.
"We focused on China because its emissions grew very rapidly during a period when there were good satellite observations of ozone available, making it much easier to see the tropospheric ozone response to changing emissions," Neu said.
In their study, newly published in the journal Nature Geoscience, researchers point out that "downward transport of naturally generated ozone from the stratosphere is an important source of tropospheric ozone in mid-latitude regions."
In other words, it's not all China's fault. But scientists say their latest analysis is proof of the importance of international cooperation in curbing atmospheric pollution levels.