In New Delhi, where an average of 1,400 new cars are added to city streets every day, the air is now dirtier than in Beijing. That’s bad news not only if you live in India, but also if you live in California or Colorado. A new study found that pollution from Asia is making smog worse in the western U.S., despite the fact that emissions from American cars are dropping.
Nitrogen oxide (NOx) pumped out of a tailpipe in India can’t travel thousands of miles, but the smog it creates can.
“The lifetime of NOx is less than one day: too short for it to travel across the Pacific Ocean,” Meiyun Lin, a Princeton University researcher and lead author of the new paper, tells Co.Exist. “However, emissions of NOx and other pollutants from cars and factories react in the atmosphere to form ozone, which has a lifetime of two to three weeks in the atmosphere–sufficiently long for ozone to travel from one continent to another continent in powerful westerly winds.”
Since 1990, nitrogen oxide emissions have tripled in Asia. The researchers looked at three decades of observations and models of pollution in the U.S.–from 1980 to 2014–and found that even though American NOx emissions have dropped by about 50%, ozone levels in rural areas have increased because of Asian pollution.
The impact in the western U.S. is highest in the spring, when weather patterns are most likely to push Asian smog across the Pacific.
Though emissions are beginning to drop in China because of aggressive measures to cut pollution, they’re growing in India, and the study predicts that their impact in the U.S. will continue to grow.
That means that if the U.S. wants clean air locally, it can’t solve the problem through domestic policy alone. “Smog pollution is a global problem,” Lin says. “A global perspective is necessary when designing a strategy to meet U.S. ozone air quality objectives.”