A numerical study of summer ozone concentration over the Kanto area of Japan using the MM5/CMAQ model

We assessed the ability of the MM5/CMAQ model to predict ozone (O₃) air quality over the Kanto area and to investigate the factors that affect simulation of O₃. We find that the coupled MM5/CMAQ model is a useful tool for the analysis of urban environmental problems. The simulation results were compared with observational data and were found to accurately replicate most of the important observed characteristics. The initial and boundary conditions were found to have a significant effect on simulated O₃ concentrations. The results show that on hot and dry days with high O₃ concentration, the CMAQ model provides a poor simulation of O₃ maxima when using initial and boundary conditions derived from the CMAQ default data. The simulation of peak O₃ concentrations is improved with the JCAP initial and boundary conditions. On mild days, the default CMAQ initial and boundary conditions provide a more realistic simulation. Meteorological conditions also have a strong impact on the simulated distribution and accumulation of O₃ concentrations in this area. Low O₃ concentrations are simulated during mild weather conditions, and high concentrations are predicted during hot and dry weather. By investigating the effects of different meteorological conditions on each model process, we find that advection and diffusion differ the most between the two meteorological regimes. Thus, differences in the winds that govern the transport of O₃ and its precursors are likely the most important meteorological drivers of ozone concentration over the central Kanto area.