The relationship between the emission of ozone precursors and the chemical production of tropospheric ozone (O3) in the Pearl River Delta Region (PRD) was studied using numerical simulation.The aim of this study was to examine the volatile organic compound (VOC)- or nitrogen oxide (NOx =NO+NO2)-limited conditions at present and when surface temperature is increasing due to global warming,thus to make recommendations for future ozone abatement policies for the PRD region.The model used for this application is the U.S.Environmental Protection Agency's (EPA's) third-generation air-quality modeling system; it consists of the mesoscale meteorological model MM5 and the chemical transport model named Community Multi-scale Air Quality (CMAQ).A series of sensitivity tests were conducted to assess the influence of VOC and NOx variations on ozone production.Tropical cyclone was shown to be one of the important synoptic weather patterns leading to ozone pollution.The simulations were based on a tropicalcyclone-related episode that occurred during 14-16 September 2004.The results show that,in the future,the control strategy for emissions should be tightened. To reduce the current level of ozone to meet the Hong Kong Environmental Protection Department (EPD) air-quality objective (hourly average of 120 ppb),emphasis should be put on restricting the increase of NOx emissions. Furthermore,for a wide range of possible changes in precursor emissions,temperature increase will increase the ozone peak in the PRD region; the areas affected by photochemical smog are growing wider,but the locations of the ozone plume are rather invariant.