Numerical Simulation Of The Impact Of Urbanization On Ozone In Shanghai

Rapid urbanization plays a tremendous impact on land-use and developing industry and increased vehicles aggravate regional air pollution. In this paper the current level of ozone(03) pollution and the impacts of urbanization in Shanghai were analyzed. In order to study the effects of land-use change and increased nitrogen oxides (NOX) emissions, the next generation meso-scale model(WRF-Chem) was run with urban canopy model(UCM) coupled. A model output system was also developed to predict O3 concentrations. The main researches and conclusions can be summarized as:(1) The current level of O3 pollution and its variation features were discussed based on observations at Luwan and Liuli. The results show that O3 pollution in Shanghai is serious and mainly occurs from April to September. The monthly and daily variations of O3 concentrations are characterized by a bimodal and double dip curve and a unimodal curve respectively. An obvious O3 "weekend effect" also exists in Shanghai. O3 concentrations have a non-linear relation to NOX concentrations. The lag time of O3 daily peak is about 5 hours. Meteorological conditions as high temperature, low humidity, slow wind speed and intensive solar radiation are favorable to O3 formation.(2) According to synoptic meteorological theory, favorable weather patterns of high concentrations are concluded by analyzing the pattern of high and low pressure systems and the relative location of Shanghai on the weather charts. The results show that high concentration O3 usually occurs when Shanghai is controlled by high-pressure and located in the uniform pressure fields with favorable upper air conditions.(3) In order to learn urbanization impacts, land-use change, anthropogenic heat and building heights were discussed based on RS data,GIS software and statistic theory. The results indicate that the urban and built-up land expanded rapidly. Anthropogenic heat emissions grow year after year, which has great impact on temperature. The average building heights of three typical urban and built-up lands are 12m,27m and 48m. The above researches can support numerical simulation later. (4) The paper also introduces the history, dynamic framework, main physical schemes, chemical mechanisms of WRF-Chem and UCM. Besides, an emission processing module was set up to prepare data for WRF-Chem.(5) The expansion of urban areas, the function of UCM, the emission of anthropogenic heat and the change of NOx emissions were considered as main aspects during urbanization. Accordingly, five sensitivity experiments were designed to run WRF-Chem for simulating three 5-day O3 episodes. The results show the urbanization caused by land-use change increases daily average O3 concentrations in urban areas, which is related to urban heat island effect, urban dry island effect and the change of surface wind fields. However, daily average concentrations in rural areas vary with different cases. The increase of NOx emission reduces daily average O3 concentrations but has few impacts on its spatial distribution.(6) O3 real-time iteration model was established based on system identification theory. It is known as a model output system(MOS). Using the observations as the forecasting value, the accuracy of level-predicted results is over 90%. Though the results using WRF-Chem output have some differences with observations, its accuracy of level-predicted results is satisfactory.Nowadays, the impact of urbanization on atmospheric environment is a hot spot of urban climate study. Numerical simulation is an effective method in this research. Though some results are obtained from the above study, further work is necessary not only to improve this paper but also for better understanding of urbanization impacts on O3.