Intercontinental transport of ozone and its precursors in a three‐dimensional global CTM

Abstract

The coupling of chemistry with atmospheric transport processes provides a mechanism for local and regional pollution from heavily populated continental regions to influence tropospheric composition at hemispheric and global scales. In this study we use the FRSGC/UCI 3‐D chemical transport model to quantify the impact of ozone precursors from anthropogenic sources in the United States, Europe, and East Asia on regional and global ozone budgets and to identify the key controlling processes. We find that the East Asian region has the greatest potential to affect tropospheric ozone due, principally, to efficient vertical transport but that Europe experiences the greatest intercontinental effects due to rapid, short‐distance transport from North America. In addition to significant boundary layer ozone production in each region, we find that 25–40% of the total net regional production occurs above 730 hPa in the free troposphere and that on a hemispheric scale, 70–85% of ozone from anthropogenic sources in the upper troposphere, above 400 hPa, is due to in situ chemistry rather than direct vertical transport. Increased surface ozone concentrations over remote continents are largest in spring and autumn at northern midlatitudes; while this seasonality is driven by horizontal transport in the free troposphere followed by subsidence, boundary layer and upper tropospheric chemical production make a substantial contribution. Although the effects are greatest in periodic episodes when meteorological conditions are favourable, there is significant enhancement in background ozone concentrations. We suggest that increasing emissions will significantly impact the oxidizing capacity of the troposphere by leading to greater polarization between ozone production and destruction environments.