Modelling tropospheric ozone production on different scales

Tropospheric ozone is currently the third most important anthropogenic greenhouse gas in terms of radiative forcing. In contrast to the long-lived greenhouse gases, e.g. CO2 and CH4, ozone has the ability to cause regional forcing, and hence regional climate change. Additionally, high concentrations of ozone occurring near the surface are harmful for humans, animals and vegetation. Within the EU countries more than 20,000 premature deaths are associated with ozone each year, and loss of arable crop production due to ozone leads to large additional costs. This thesis is concerned with the impacts of tropospheric ozone on scales ranging from urban to global, as well as interactions between these scales. Two numerical atmospheric models have been applied; the regional WRF-Chem model and the global Oslo CTM2 model. In order to investigate scale interactions in ozone formation, several simulations were carried out using various resolutions of megacity emissions. A change in megacity emission resolution induced small-scale spatial changes in ozone fields, but relatively small changes when integrating over a large volume. Thus, this study suggests that high resolution is more important for local air pollution studies than for large scale ozone changes relevant for climate studies. European measurements and model simulations both show that concentrations of the ozone precursor NO2 have declined over the last decade, while the trend in near-surface ozone is more moderate. Part of the reason for this non-linear response is the strong sensitivity of ozone to meteorological processes, as it is a secondary pollutant and not directly emitted. Global simulations for the future show that emissions from aircraft and ship traffic will likely have larger impacts on the atmospheric chemical composition in the future. However, there is a potential of reducing the ozone warming effect from aircraft by nearly 30% in 2050, purely by technological improvements. Potential impacts of climate change on regional air pollution were estimated. First, extreme summer episodes were investigated with particular focus on the hot summer of 2007 in the Eastern Mediterranean. It was found that elevated near-surface ozone levels during this period were mainly caused by high temperatures leading to increased biogenic emissions of ozone precursors and less uptake of ozone by vegetation, along with substantial contributions from forest fire emissions in Greece. Second, global atmospheric chemistry simulations with climate data for the future show that important changes in the near-surface ozone distribution may take place in some regions, particularly in South Asia and in the Eastern Mediterranean. Although most regions show stronger ozone responses due to expected changes in emissions, the impacts of climate change on ozone should not be neglected