Faculty of Science and Technology

Atmospheric Science Theme Seminar

Changing anthropogenic emissions of ozone precursors are likely to lead to future changes in surface ozone over many parts of the globe. This study describes a simple parameterization to estimate surface ozone changes due to past or future changes in anthropogenic precursor emissions based on results from 14 global chemistry transport models. The method successfully reproduces the results of full simulations with these models. For a given emission scenario it provides the ensemble mean surface ozone change, a regional source attribution for each change, and an estimate of the associated uncertainty as represented by the variation between models. Using the new Representative Concentration Pathway (RCP) emission scenarios as an example, we show how regional surface ozone is likely to respond to emission changes by 2050 and how changes in precursor emissions and methane contribute to this. Surface ozone changes are substantially smaller than expected with the SRES~A1B, A2 and B2 scenarios, and this reflects the assumptions of more stringent precursor emission controls under the RCP scenarios. The study reveals the increasing importance of limiting atmospheric methane growth as emissions of other precursors are controlled, but highlights differences in modelled ozone responses to methane changes of as much as a factor of two, indicating that this remains a major uncertainty in current models.