Abstract

Long-term observations in different parts of the world indicate that the abundance of ozone in the troposphere is increasing. As ozone is a strong oxidant and a greenhouse gas, this has important implications for surface air quality, for the oxidative environment of the troposphere, and for climate. Reproducing these trends in chemistry-transport models has proved difficult, reflecting uncertainties in our understanding of emissions, chemical processing and important transport and mixing processes. While it is clear that increased anthropogenic emissions of ozone precursors are largely responsible for the observed changes in ozone, current models cannot represent the different regional trends in ozone, suggesting that natural dynamical processes (transport and stratosphere-troposphere exchange) and biospheric interactions (biogenic hydrocarbon emissions, biomass burning and land-use change) also have important roles to play. While a full assessment of the interactions between the atmosphere, biosphere and climate system awaits the upcoming generation of Earth System models capable of resolving these feedbacks, this talk describes recent studies exploring the strengths and weaknesses in our current understanding of how emissions and meteorological processes control tropospheric composition.