Modelling of atmospheric oxidants and aerosols: deposition, emission and chemical transformation / QUEST

The earth system is comprised of a large number of interacting components. For example, the atmosphere is controlled not just by processes occurring in situ but also by fluxes of energy and a variety of chemical species from the land and ocean surfaces. Similarly, atmospheric composition also depends on deposition to the earth surface. Furthermore, these processes are all likely to change with the climate state. It is only recently that detailed chemical schemes have been included in the best climate models. Coupling between land surface processes (emissions, deposition, etc.) and the chemistry/climate system has been introduced into numerical models, albeit somewhat simplified. These latter interactions could however be very important for composition and climate. The time in now right for a major UK initiative within NERC's QUEST programme, to study the role of surface processes on atmospheric oxidizing capacity and aerosol loading, building on an initiative already underway between the Met Office and the NERC Centres for Atmospheric Science (NCAS) to develop a new community model, UKCA, to study the interaction between climate and composition (gas phase composition and aerosols). This proposal addresses that task. Our proposal brings together relevant UK expertise with four main foci. These are (1) the development and testing of chemistry and aerosol schemes to include in a climate model, (2) the development and testing of a range of schemes to describe (interactively wherever possible) surface emissions of reactive trace gases, (3) the development and testing of new surface deposition schemes, and (4) implementation of these schemes into the climate model which will be used to look at climate-related variability of the model system for the immediate past and the near future. This will allow the interaction between changing climate and surface emissions with full description of the feedbacks occurring within this system. Changes in the output of the climate model will affect emissions directly, as changes in temperature, soil moisture and light intensity have direct effects on the emission rates of biogenic volatile organic compounds (VOCs). These emissions (for example, the strongly temperature-dependent isoprene emissions) can affect oxidizing capacity, and hence tropospheric OH and so the concentration of reactive greenhouse gases, including ozone, thereby completing the feedback loop. Second-order effects may also be important, for example, changes insoil moisture or elevated ground level ozone may also alter VOC emission rates. Our study will allow these chemistry/climate feedback processes to be assessed in studies covering the last century and the coming century.