Intercontinental Transport of Ozone and its Precursors in a 3-D Global CTM

Oliver Wild, Hajime Akimoto

Journal of Geophysical Research, 106 (D21), 27,729-27,744, 2001.


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 paper 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. While there is significant ozone production in the boundary layer over each region, there is also considerable enhancement in ozone in the free troposphere due to both direct vertical transport and to chemical formation from transported precursors. We find that 25-40% of the total regional net 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 transport. Horizontal transport in the free troposphere followed by subsidence leads to enhanced ozone concentrations over remote continents, and we find that these are largest in spring and autumn for Northern mid-latitude regions, and that boundary layer and upper tropospheric chemical production play important roles in modulating this transport signal. While the effects are greatest in periodic episodes when meteorological conditions are favourable, we find significant enhancement of background ozone concentrations. 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. 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.