Increasing springtime ozone mixing ratios in the free troposphere over western North America

High concentrations of ozone in the troposphere are toxic and act as a greenhouse gas. Anthropogenic emissions of ozone precursors have caused widespread increases in ozone concentrations since the late 1800s, with the fastest-growing ozone precursor emissions currently coming out of east Asia. Much of the springtime east Asian pollution is exported towards western North America; a strong increase in springtime ozone mixing ratios is now found in the free troposphere over this region.