Atmospheric Chemistry and Physics

Abstract. The EMEP4UK modelling system is a high resolution (5×5 km2) application of the EMEP chemistry-transport model, designed for scientific and policy studies in the UK. We demonstrate the use and performance of the EMEP4UK system through the study of ground-level ozone (O3) during the extreme August 2003 heat-wave. Meteo-rology is generated by the Weather Research and Forecast (WRF) model, nudged every six hours with reanalysis data. We focus on SE England, where hourly average O3 reached up to 140 ppb during the heat-wave. EMEP4UK accurately reproduces elevated O3 and much of its day-to-day variabil-ity during the heat-wave. Key O3 precursors, nitrogen diox-ide and isoprene, are less well simulated, but show generally accurate diurnal cycles and concentrations to within a factor of ∼2–3 of observations. The modelled surface O3 distribu