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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.