Ozone is a key component in smog and is also a contributor to global warming. In terms of impact on global warming, it ranks behind carbon dioxide and methane as the third greatest contributor. Areas such as California suffer from ozone pollution that causes smog, but not just their own ozone.

A study recently published in the journal Nature has detailed the sources of ozone on the United States’ west coast. The study was performed by researchers at the University of Colorado alongside National Oceanic and Atmospheric Administration’s Earth System Research Laboratory in Boulder, Colorado.

Air samples between 1995 and 2008 were used in order to determine the amount of ozone and the source of the ozone. Thousands of air samples were used in total, concluding that ozone has seen an overall increase of 29 percent during this time frame.

Ozone from Asia is contributing to the increase of ozone in these areas, especially the ozone in the troposphere, which is two to five miles in altitude. This is not completely surprising as many pollutants make their way from Asia to the United States. However, this was the first definitive study on ozone coming from Asia to the U.S. west coast.

Other pollutants which make their way from Asia are mercury, PCBs and soot. The pollutants have increased alongside the economy in the area, especially China’s economy. The pollutants, however, come from other countries in addition to China, including India, Vietnam, Laos and Cambodia. Ozone was traced back to these countries in the study as well.

Lead author of the study, Owen Cooper, stated: “The important aspect of this study for North America is that we have a strong indication that baseline ozone is increasing. We still don’t know how much is coming down to the surface. If the surface ozone is increasing along with the free troposphere ozone, that could make it more difficult for the U.S. to meet its ozone air quality standard.”

The researchers have indicated that future studies will involve ground level ozone and the original sources of the ozone.