Many of the measures taken by federal, state and local administrations in the United States to improve air quality on its West Coast are being thwarted by air pollution blowing across from China. This is the conclusion of research conducted by Wageningen University in association with the Royal Netherlands Meteorological Institute (KNMI) and the American space agency NASA, recently published in Nature Geoscience.
Nitrogen oxide emissions from traffic and industry in combination with ample sunlight induce ozone smog. This smog causes respiratory irritation, damages crops, and is an important greenhouse gas. The US governments strive to reduce emissions by stimulating cleaner cars and introducing prohibitive measures in industry. Their efforts led to a 20% drop in the production of ozone-forming nitrogen oxides on the American West Coast between 2005 and 2010. “Curiously, this drop did little to improve the local air quality, particular in terms of ozone reduction,” says Willem Verstraeten, researcher at Wageningen University and KNMI.
According to research carried out by Verstraeten and his colleagues, the main culprit is the sharp economic growth in China, on the other side of the Pacific Ocean. While nitrogen oxide emissions in the western United States were decreasing, in China they were increasing; the level of ozone above China rose by 7% in a short period. Willem Verstraeten: “The dominant westerly winds blew this air pollution straight across to the United States. As a manner of speaking, China is exporting its air pollution to the West Coast of America. This was demonstrated using global satellite measurements of nitrogen oxide and ozone. These observations in combination with a chemistry transport model enabled us to establish the causes of increasing ozone levels and analyse intercontinental transport of ozone pollution for the first time ever.”
These findings show that reducing air pollution requires both local and global measures. In the Netherlands too, air pollution is partly caused by neighbouring countries and air arriving from across the sea. According to estimates, half of our ozone is imported from elsewhere. More than a quarter originates from North America, almost 15% from the Asian continent and just 10% from the stratosphere. Willem Verstraeten: “Local measures to improve air quality certainly help, but the real solution lies in a global strategy.”
Read the full article: ‘Rapid increases in tropospheric ozone production and export from China’