Study Of Atmospheric Particulate-cloud-radiation-photochemical Process On Ozone In Nanjing

In recent years, due to continued economic development, rapid expansion of urban area, and increasing number of motor vehicle, air pollution caused by industrial emissions, vehicle exhaust and construction dust becomes more serious in Nanjing. Atmospheric particulate and ozone, as known important air pollutants, have serious impacts on air quality and human health, and particulate may affect the ozone formations due to the cloud and radiation processes. As the important industrial city of the Yangtze River Delta region and the host city of the second Youth Olympic Games in 2014, air quality of Nanjing becomes the focus of attention from all walks of life. So it can be useful to understand forming mechanism in pollution of Nanjing, and provide a good reference to formulate reasonable air pollution control scheme for the government by carrying out the study of atmospheric particulate on ozone.In this study, focus on atmospheric particulate-cloud-radiation-photochemical process on ozone, relying on data analysis, mechanism research and numerical simulation to explore possible ways and relative contribution of particulate-radiation-photochemical process and particulate-cloud-photochemical process, which emphasizes analysis about internal mechanism and main influencing factors of particulate-cloud-photochemical process. Research work and conclusions are as follows.Firstly, preliminarily understands the relevant characteristics of atmospheric particulate-cloud-radiation-photochemical process on ozone by analyzing the observation data from April 6 to April 10,2012. Based on analysis of this typical case, PM2.5 concentration had a big difference with ozone from April 7 to 8. PM2.5 concentration increased almost 25μg/m3, with an increment from 1.09 to 1.35 and 1.94 to 7.25 appeared in the aerosol optical depth and cloud optical depth respectively, leading to the volume mixing ratio of ozone and ultraviolet radiation flux reducing 6 ppb and 7W/m correspondingly at Gulou station. Simultaneously, PM2.5 concentration increased almost 14μg/m3, resulting in a decrease of 49 ppb in ozone at Caochangmen station. Results show that two processes of atmospheric particulate could significantly weaken the incident UV radiation and the atmospheric photochemical oxidation reaction rate, which leads decrement in ground-level ozone concentration eventually when meteorological condition and ozone precursor keep stable with gradual development of cloud.Secondly, a box model has been employed to investigate the internal mechanism that how atmospheric particulates affect ozone. Results of control experiment show that particulate-radiation-photochemical process reduces HOx, O3, ASO4 and ANO3 concentration with 0.36ppt,8.02ppb,0.17 and 0.11μg/m3, respectively, and particulate-cloud-photochemical process reduces HOx, O3, ASO4 and ANO3 concentration with 0.10ppt,2.13ppb,0.04 and 0.13μg/m3, separately, when given with fixed value of cloud fraction and PM2.5 concentration, such as 5 and 50μg/m3. Particulate-radiation-photochemical process is stronger than the other one significantly, but both of them have little influence on secondary inorganic aerosol. Considering the variation of PM2.5 concentration, the rate of HOx, O3, ASO4 and ANO3 in the two processes of particulate are -0.0349 and -0.0038ppt/(10μg·m-3),-0.895 and -0.083ppb/(10μg·m-3),-0.0179 and -0.0017μg·m-3/(10μg·m-3),-0.0113 and-0.0012μg·m-3/(10μg·m-3), respectively. In addition, with increasing cloud fraction and stable PM2.5 concentration, particulate-cloud-photochemical process will first strengthen and then decrease O3 consumption.Finally, regional air quality model system CMAQ has been used to analysis these two processes of particulate on ozone and other trace components. Simulation suggests that both of these two processes, which mainly play a role under the altitude of 3 kilometers, would decrease the concentration of HOx, O3 and ASO4. But the variation of concentration in ANO3 caused by the impacts is complex. Particulate-radiation-photochemical process is dominant over Nanjing. During the height interval of 0～1km, decrement of HOx, O3, and ASO4 due to particulate-radiation-photochemical process are 6.43%,2.69%, and 2.00%, respectively, while that due to the other one are 0.46%,0.18%, and 0.13%, respectively. So the decrement in ozone by particulate-cloud-photochemical process is almost 6.7% of the other.Based on study of observations and models, particulate-radiation-photochemical process is stronger than the other significantly, but both of them will decrease ozone concentration in Nanjing. So it can provide scientific basis on controlling urban atmospheric particulate and ozone.