Application Of Four Dimensional Data Assimilation And Three Dimensional Footprint Model In Atmospheric Environmental Study

Under the fast growth of the urbanization and industrialization, the atmospheric pollution becomes a serious problem in the Pearl River Delta Region these years, and has caused negative effects on the human health and life. Otherwise, duo to the densely distributed cities, there would be high concentration of pollutant release and they would disperse, transport and accumulate among each city, adding the complexity of the pollution problem. As a result, it is very important to study the diffusion and transport of pollutants in order to improve the urban air quality, environmental planning and development. With the observation data from the Pearl River Region Campaign on October, 2004, this paper works on the properties of some air pollutants and their corresponding source areas, and designs a methodology to calculate the pollutant source distributions from an observation network.To simulate a more accurate wind field for atmospheric diffusion and transport, a meso-scale meteorological model is used, accompanied with Four Dimensional Data Assimilation. The results are optimized with IAU (Incremental Analysis Updates) to damp the high-frequency oscillation. After verification, the output is more similar to the real-time observation, which reflects the true condition of the air-flow field.The on-line combination between meteorological model and random-walking dispersion model has been completed, which reduces the uncertainty of model results. The 3-dimensional footprint function is applied to calculate the potential pollutant source area over different heights. The results show that under windy condition, the footprint structure follows straight with the corresponding wind direction and the terrain forcing effect is obvious; while under other conditions, the footprint is sparsely distributed over a large area. During the case of air pollution, the major footprint (>0.005×10^-6 s/m³) is always below 1000 m and the high-level footprint only has a small contribution (<=5%), demonstrating that the pollutants are mainly released by ground sources and tall stacks and accumulate in the boundary layer, which is the cause of the high concentration near ground. As the ground footprint, the contributions from different land covers (urban and natural types) are analyzed. Taking Guangzhou as an example, the footprint contribution from urban is larger than those from other land types; while in the natural types, the contributions from forest and plantation are the major part, consisting together more than 10% of the total footprint, and reaching 20% during air pollution. The area footprint distribution for Pearl River Region is also calculated, in which three pollutant transferring routes can be found, including southwards from Conghua; southwestwards from Dongguan; and westwards from east bank of Pearl River Estuary.The analysis of observation shows that the major pollutant in Pearl River Region is PM10. The main source areas for SO₂ are Foshan and the power-plant region along the Pearl River Estuary. In Guangzhou, the high concentration accompanied with the southwestern or eastern wind, while in Xinken, with the northeastern or southeastern wind. The SO₂ pollution in Guangzhou is caused mainly by pollutant transportation, but the reason for PM10 is more complicated, including both the effects from local release and regional transfer.The results of footprint model are verified with the source strength data from the 2004 TRACEP Experiment. After comparison with the observed concentration, the SO₂ simulation seems much better in both the trend and magnitude than that of PM10. The PM10 simulation is good in windy condition, but would have twice error in other conditions.The above results prove that the footprint method can effectively interpret the information of potential source area from single or multiple observations, which would be a good tool for reference in environmental supervision and management. As the concern of air pollution keeps growing and the observation network increases, the footprint analysis method would be very practical when applied in the environmental study.