| With the development of industry and economy, city extends and polulation and cars grows, which leads to the greater demands on fossil fuels and severer pulution on air. The air pollution not only damages the environment, but also threats to human health, and affects the ecosystem balance, and even change climate. As the host for2014Olympic Young, the air quality in Nanjing receives more and more attention. Therefore, accurate and effective forecasting on Nanjing’s air quality is especially important. Based on the observational data, the spatial and temporal distribution of the major air pollution in Nanjing is studied. A new generation of meteorological and chemical model WRF/Chem is used to establish the Air Quality Forecasting System in Nanjing. A process of air pollution cased by straw burning is analysed and simulated by numerical model. The major work and results are as follows:Respirable particulate matter (PM10), ozone (O3), sulfur dioxide (SO2), carbon monoxide (CO) and nitrogen oxides (NOx) are main air pollutants in atmosphere. PM10will remain suspended in the air and reduce visibility, will also enters human body through the respiratory system produce harm to health. O3plays an important role in the atmospheric and ecological environment, as an important oxide participating in photochemical processes. CO, SO2and NOx have also significantly impact on atmospheric environmental, water and soil. In this study, Observed data are used to investigate the spatial and temporal characteristics of air pollutants in Nanjing; A new generation air quality modeling system (WRF/Chem) in which the meteorological and chemical processes are fully coupled online, are used to build air quality forecast system.Based on surface observations of PM10, O3, SO2, CO and NOx at eight sites (shanxilu, maigaoqiao, xuanwuhu, ruijinlu, zhonghuamen, caochangmen, pukou, njupukou) in Nanjing during the period from2007to2009, the variations of air pollutants on different time scales (hourly, daily, weekly, monthly) and spatial characteristics and their relationships are studied through statistical method. Investigations show that PM10is the dominant pollutants in Nanjing around0.1mg/m3。About85days (38days) and91days (54days) are over polluted of NO2and PM10in ccm (pk), with11.9%(5.97%) and12.8%(8.22%) of the total during the observation period in2008and2009. Concentrations of PM10and NOx exhibit two peaks at8am and20pm, while SO2shows peaks at9or10am in the morning. Clear diurnal pattern is observed for O3concentration with maximum14pm in the afternoon and low level at night. Concentrations of NH3are low in autumn and winter and high in spring, while concentrations of PM10and SO2are high in autumn and winter and low in spring. In addition, O3level is lower at weekdays compared to weekends, while SO2, CO, NOx concentrations are higher at weekdays than those on weekends. The backward trajectory cluster analyses indicated that local sources make a great contribution to the air pollutants arriving at Nanjing, but long range transport also plays an important role in the seasonal variations of the air pollutants. As affected by the Southeast wind in summer, the maritime air masses are relatively clean, while the cold northern air masses with high pollutant level dominate in winter. The local sources have significant impact in winter, which are higher compared to other kind of air masses.Based on WRF/Chem model, with the emission inventory of PM10,SO2and NO2in Nanjing, two months retrospective forecast and four months real time forecast starting from Jan1,2010are evaluated by Air quality forecast system. The result shows the simulated surface pressure, temperature and wind speed are higher than observed. In the retrospective forecast, The accuracy rate of the prediction on urban air quality index are61%,76%and97%, respectively. four months’real time forecast result show that the accuracy rate of the prediction on urban air quality index is60%。Investigations show that WRF/Chem performed good in urban air quality forecast on SO2, NO2and PM10. It is suggested that the improvement of the emission inventory from fugitive dust, transportation and biomass burning are necessary to get better performance on air quality prediction.Satellite remote sensing data, surface meteorological and air pollutants observations, air pollution index, MICAPS data and the backward trajectory analyses were used to investigate a serious air pollution event took place in Nanjing and surrounding regions during Nov.7and Nov.82009. the atmospheric conditions and planetary boundary layer (PBL) features. The results showed that low shear and weak convergence in atmospheric boundary layer, sparse isobar, low wind speed/calm wind, are not convenience for air pollutants dispersion. On the other hand, inversion layer confined the pollutants in the mixing layer and high relative humidity was in favor of the formation of haze, intensifying air pollution. The transport of gas pollutants releasing from crop residue burning around Nanjing and north parts of Jiangsu Province, combining with unfavorable weather condition, which was the dominating reason of this air pollution episode. |
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