Multiscale Modeling of Multi-decadal Trends in Ozone and Precursor Species Across the Northern Hemisphere and the United States

Multi-decadal model calculations for the 1990–2010 period are performed with the coupled WRF-CMAQ modeling system over a domain encompassing the northern hemisphere and a nested domain over the continental U.S. Simulated trends in ozone and precursor species concentrations across the U.S. over the past two decades are compared with those inferred from available measurements during this period. The model results suggest large and contrasting changes in tropospheric composition over the northern hemisphere with significant reductions in air pollution over North America and Western Europe and increase in large portions of Asia. The model is able to capture the changing seasonal distributions in surface O3 in the U.S. during 1990–2010 arising from changing emissions and long-range transport.