Numerical Simulation Of Ozone In Shanghai

The rapid development of human society makes the environmental problems more and more notable, of which the urban air pollution is one of the most important problems. Air pollution like ozone excess and haze commonly occurred in Shanghai, the most economically developed city of China and the host city of the World Expo 2010.This paper analyses statistically on the ozone pollution in Shanghai during the World Expo 2010, based on which, the mesoscale numerical model WRF-Chem coupled with urban canopy model (UCM) was used to do numerical simulation research on the pollution cases and sensitivity test on the emission of NOx,VOCs and regional pollutants. The main researches and conclusions can be summarized as:(1) According to the statistic analysis of pollutant concentration diurnal variations the results were got, the diurnal variations of ozone concentrations are characterized by a unimodal curve with the minimum and maximum concentration occurred at 5-6 o'clock and 14 o'clock respectively. There is a good consistency between particles and the diurnal variation of NOx, both of which show a double-peak under the effects of vehicles in rush hours. Concentrations of evening peak are lower than those of morning peak, while time and peak concentrations of pollutants differ among stations. A negative correlation was found between NOx and O3 concentrations in diurnal variation as peak concentration of NOx appears earlier than O3, with the lag time being less than 5hours, during which NOx was consumed by a series of photochemical reactions with solar radiation. Meanwhile, quantities of O3 were generated rapidly. In a word, NOx laid material conditions for the generation of O3.(2) WRF-Chem numerical model was used to simulate 4 high concentration ozone pollution events, and the relationship between ozone pollution and meteorological elements such as wind, temperature, humidity and so on was also discussed. The results show that the numerical model has a strong ability of simulating meteorological field. Meanwhile, ozone simulations and observations have a good consistency; the simulations of NOx and PM2.5 concentrations are nearly coincide with observations at Jingan station sitting in urban area. But the simulations in suburban stations are obviously lower than observations. In addition, Meteorological elements play an important role in ozone concentrations variation. Strong shortwave radiation, high temperature and low humidity are favorable to O3 formation. High wind speed has diffusion effect in ozone variation, and the distribution of ozone tend to downwind direction along with the wind field changes. There is a good consistency between ozone special distribution and meteorological fields like temperature field, humidity field and wind field. High ozone concentration area matches high temperature, low humidity and wind convergence zone.(3) Several sensitivity experiments were done by using WRF-Chem to research the effects on ozone concentrations with different emission of NOx and VOCs. The results of the sensitivity experiments shows that, based on the recent emission list, keeping VOCs emission constant the ozone concentrations reduce as NOx emission increases, while keeping NOx emission constant the ozone concentrations increases as VOCs emission increases, which means the ozone generation in Shanghai is more sensitive to VOCs emission than that of NOx. Furthermore, in order to study the ozone transport in vertical space a contrast test was added. The results show that the ozone exchanges in vertical space are different at different time and places, and the exchange is strongest at noon. That is because uneven surface heat distribution due to solar radiation leads to different local turbulence.(4) In order to study the regional transport of ozone, several scene experiments were done with different emission reduction schemes by using WRF-Chem numerical model. The experiments show that the emission reduction of pollutants in surrounding areas of Shanghai can effectively reduce the ozone concentration in Shanghai, especially the concentration peak. With different wind field, the ozone concentration appears various reactions to emissions of different direction, of all directions emissions from upwind have the greatest contribution to local ozone concentrations. Meanwhile, the influence of pollutant emission varies to the distances from Shanghai center. The pollutant emissions of Shanghai surrounding area have more effect on Shanghai suburban districts than Shanghai urban districts. The scene experiments well present the impact of pollutant emissions emitted by surrounding areas on the local ozone concentrations in Shanghai, under the background of wind field. It provides scientific research approaches for the establishment of regional emissions reduction measures.