Asian emissions increase ozone over North America
Increases in tropospheric ozone levels above western North America during springtime are due to eastward air flows across the Pacific Ocean, with the largest increases associated with air that comes from South and East Asia, according to a recent study.
In the troposphere, the lowest layer of the atmosphere, increased levels of ozone are considered to negatively affect human health and vegetation, including crop production. Ozone also contributes to the greenhouse effect, ranking behind carbon dioxide and methane in importance.
While emissions in Europe and the Unite States of the main ozone precursor, nitrogen oxides (NOx), have decreased over the last 10–20 years, they have increased in China and other parts of Asia.
Springtime ozone values above western North America were found to have increased by 14 per cent during 1995–2008, and evidence suggests a similar rate of increase has occurred since 1984. The study determined that, as average ozone values increased, the origin of the transported air moved even further to the west, with the largest increases in ozone values associated with dominant airflows from south and east Asia.
Source: Science for environmental policy, European Commission, DG Environment, 25 February 2010. Study: Increasing springtime ozone mixing ratios in the free troposphere over western North America. By O. R. Cooper, D. D. Parrish, A. Stohl, et al. (2010). Nature. 463: 344–348.