A numerical study of influences of urban land-use change on ozone distribution over the Pearl River Delta region, China

Atmospheric dynamical and chemical models are conducted to explore impacts of urban land-use change on ozone concentrations over the Pearl River Delta (PRD) region, China. Two scenarios of land-use distributions are used to represent early 1990s and current urban land-use distributions. Urbanization increases 2-d averaged daytime (nighttime) temperature by 0.8°C (1.5 °C) and reduces wind speed by about 20% over the PRD urban areas. The daytime boundary layer depth is up to 400 m deeper, while there is a 50-m increase during nighttime. The combination of these seemly subtle changes in meteorological conditions is able to prompt detectable changes in surface O₃ concentration (4.15 ppbv) over major PRD urban areas. Nighttime O₃ concentration enhancement is greater than daytime in the urban expansion regions (e.g. 10 ppbv daytime and 15 ppbv nighttime). Areas with main O₃ concentrations increase coincide with the areas of increased temperature and decreased wind speed, and the timing of maximum ozone concentration increase occurs a few hours later than maximum temperature increase and wind-speed reduction. Moreover, planetary boundary layer depth also plays an important role in modulating vertical transport of O₃, which can lead to daytime surface ozone concentrations reduction in some regions even with increasing temperatures.