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Stratosphere-Troposphere Exchange and Troposphere Ozone Variability

Tropospheric ozone variability results from complex and mutually dependent interactions between meteorology, precursor emissions, photochemistry, and Stratospheric-Tropospheric Exchange (STE). An explanation for the interannual trends and variability in tropospheric ozone over the last few decades has proven elusive despite the regulatory need to establish clear links between changes in tropospheric ozone and changes in ozone precursor emissions and climate. In this talk I evaluate the interannual variability and trends in tropospheric ozone between 30 and 90o N from1990-2009 using ozone measurements and a global chemical transport model. Both the model and measurements indicate that on large spatial scales STE has driven significant tropospheric variability at 500 hPa as well as at the surface and contributed significantly to long-term tropospheric ozone trends.