Wednesday, 17 January 2007: 9:15 AM
A Numerical Study of Influences of Land-Use Change on Chemical Species over the Pearl River Delta Region, China
212A (Henry B. Gonzalez Convention Center)
The Pearl River Delta (PRD) region, an area of about 41,700 km2 located in the southern part of Guangdong Province in China, has experienced remarkable economic development and urbanization in the past two decades. Urban areas account for 60% in the total land use, which is two times higher than the Chinese national averaged level. Urbanization can significantly modify local and regional meteorological conditions, and hence impact air dispersion and quality. In this paper, numerical simulations with a mesoscale atmospheric model and a chemistry models are conducted to explore the impacts of land-use change on chemical species for a high-pollution episode over the PRD region. Two scenarios of land-use maps are used to represent late 1980s (i.e., prior to significant urbanization) and today's urban distribution in PRD. Results show that averaged over a 48-hour time period, urbanization increases (decreases) temperature (water vapor mixing ratio) by roughly 5% and reduces wind speed by about 25%. More pronounced changes in meteorological conditions occur in late evening and near the surface. These changes in meteorological conditions together result in detectable changes in chemical species, leading to higher O3, OH and PAN concentration, and lower NOX over major PRD urban areas.. Primary pollutants (SO2, NOX) have the same diurnal trend, but the urban land-use change has larger influences on NOX than on SO2. Daytime temperature augmentation (larger in vertical extent but smaller in magnitude compared to its nocturnal increase) merely affects chemical species. Large O3 and NOX variations from late evening to midnight can reach as high as 1000 m, because the urban heat island de-stabilizes the stable nocturnal boundary layer.