Air pollution from China, India and several other Asian countries has wafted across the Pacific Ocean over the past 25 years, increasing levels of smog in the western US according to recent research. 1
Smog, also know as ground level ozone, is harmful to human health because it can exacerbate asthma attacks and cause difficulty breathing. It also harms sensitive trees and crops.
Since 2000 smog forming emissions have decreased by approximately 50 percent in the US due to Clean Act Air enforcement, pollution controls on large emitters and regulations on cars and trucks.
Yet in the rural West where most national parks are located ozone levels haven’t dropped. That’s because these areas are usually higher elevations and closer to the layers in the atmosphere where smog travels over from Asia. 2
One example is Joshua Tree National Park, whose desert terrain ranges from 934 to 5,800 feet. There, rising emissions from Asia have actually offset Southern California’s efforts to combat smog. Emissions of nitrogen oxide, a precursor to ozone, have fallen 30 percent in greater Los Angeles since 2000, yet springtime ozone levels at Joshua Tree held steady from 1990 to 2010. 1
Some higher elevation western cities are also more susceptible. For instance Denver is one example: there ozone levels have remained stubbornly high despite significant local reductions in smog forming emissions.
Scientists measured ozone levels recorded at springtime for the past 25 years in 16 national parks in the western US, incluiding Yellowstone, Yosemite and Grand Canyon. The parks’ locations, farther away from cities where smog is typically expected, made them ideal spots for a study. The team looked at levels in the spring when wind and weather patterns push Asian pollution across the Pacific. In the summer, when those weather patterns subside, ozone levels in the national parks remained well above normal. 3
In the springtime ozone levels in the national parks rose by 5 to 10 parts per billion (ppb), which is significant given that the federal ozone standard is 70 ppb. 4
Another study on the Sierra snow pack confirmed that more than a third of the air pollution affecting California originates in China.5
Since 1992 Asia has tripled its emissions of smog forming chemicals such as nitrogen oxides. Though China and India are the worst offenders, North and South Korea and Japan also contribute. 3
Despite a 50 percent cut in smog forming chemicals such as nitrogen oxides over the past 25 years, ozone levels measured in rural ares of the west have actually climbed. Clearly, the influx of pollution from Asia makes it difficult for these areas to comply with the federal ozone standards. 4
Researchers also looked at other contributors to ground level ozone such as global methane from livestock and wildfires. Wildfire emissions contributed less than 10 percent and methane about 15 percent of the western US ozone increase, while Asian air pollution contributed as much as 65 percent. 4
Asian pollution only slightly contributes to smog in the eastern US. Levels there typically spike during intense summer heat waves.
Extreme air pollution in Asia is also affecting the world’s weather and climate patterns. Using climate models and data collected about aerosols and meteorology over the past 30 years, researchers found that air pollution over Asia—much of it coming from China—is impacting global air circulations. This pollution affects cloud formations, precipitation, storm intensity and other factors and eventually impacts climate. 6
China’s booming economy during the last 30 years has led to the building of enormous manufacturing factories, industrial plants, power plants and other facilities that produce huge amounts of air pollutants. Once emitted into the atmosphere, pollutant particles affect cloud formations and weather systems worldwide.
Air pollution levels in some Chinese cities, such as Beijing, are often more than 100 times higher than acceptable limits set by the World Health Organizations standards. 7
Ozone is only one of many pollutants from Asia that reach the US. Instruments regularly detect mercury, soot, and cancer causing PCBs. At present China emits more sulfur dioxide than any other country in the world. All this contributes to the ‘Asian Brown Cloud” which covers an area as large as Australia, obscuring the sun in some polluted Asian cities. At times, it drifts across the Pacific Ocean and covers the Northern Hemisphere. 8
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