A study has found that over the past 25 years, air pollution from China, India, and several other Asian countries has wafted across the Pacific Ocean which led to an increased level of smog in the western U.S.
Smog (ground-level ozone) is harmful to human health as it can aggravate asthma attacks and create difficulty breathing. It also hurts sensitive crops and trees. Unlike the good kind of ozone which is in the stratosphere, that protects life on Earth from the sun’s harmful ultraviolet rays.
For the past 25 years, scientists have measured ozone levels during springtime in 16 national parks in the western U.S., The parks, such as Yellowstone, Yosemite and Grand Canyon, are ideal spots for the study as they are the farthest away from cities, where smog usually could be found.
According to Meiyun Lin a scientist at the National Oceanic and Atmospheric Administration who led the study, the researchers studied ozone levels in the springtime when wind brings pollution from Asia to the US across the Pacific Ocean. When those weather patterns decrease in the summer, ozone levels in the national parks remained above normal.
Asian polluters are to blame:
The researchers have found that the highest contributor to smog in the West is by far Asian air pollution. Other factors like methane from livestock and wildfires, were also studied by the team. They have found that western U.S. ozone increase was due to Asian air pollution by 65% while methane contributed by 15% and wildfire caused less than 10%.
Emissions of smog-forming chemicals such as nitrogen oxides have tripled in Asia since 1992. China and India are the biggest polluters but North and South Korea and Japan also contribute
Despite a 50% decrease in U.S. emissions of smog-forming pollutants, smog levels in the western U.S. kept on increasing every year.
Owen Cooper, a senior research scientist at the University of Colorado and NOAA said: “Twenty years ago, scientists first speculated that rising Asian emissions would one day offset some of the United States’ domestic ozone reductions,” although Cooper was not directly involved in the study, his prediction has come true.
The study has found that in the eastern U.S., Asian pollution only slightly contributes to smog. Levels only increase during strong summer heat waves.