The Mechanism Of Photochemical Smog Formation And Its Mitigation

Photochemical smog is composed of ozone,Peroxyacetyl nitrates (PAN) and nitric acid (HNO3) pollutants which are formed by some photochemical reactions of nitrogen oxides and hydrocarbons under ultraviolet ray radiation.In order to understand the impact of vehicle exhausts on photochemical smog in city and the relationships among the pollutant concentrations during photochemical fog formation reaction, the photochemical smog formation mechanism is explored firstly, and the current pollution levels and developing trends of exhaust pollution in big city are discussed. Then the simplified set of photochemistry dynamic equations is established, and a numerical simulation of photochemical smog formation at different initial conditions is carried out. We can summarize the prevention and cure measure of photochemical smog pollution . Finally the Empirical Kinetics Modeling Approach graphs of ozone and PAN are plotted, and the mitigation measures of photochemical smog pollution in different kinds of cities are proposed. The conclusions are summarized as follows:1.The index of photochemical smog pollution grade in city is established. Using the ratio of NOX to SO2, it is concluded that the urban air pollution characteristic in this country is being transformed to the exhaust type of motor vehicle (photochemical smog type) from the soot type.2.The formation process of photochemical smog is numerically simulated using the explicit Runge-Kutta method and the MATLAB tool, the numerical simulation of photochemical smog formation process is carried out based on the simplified photochemistry dynamic model. It can also be seen from the simulation results that under the condition of low concentration ratio of NMHC/NOX, when the initial concentration of NOX is fixed, increasing NMHC leads to increasing O3 and PAN. While initial concentration of NMHC is fixed, increasing NOX results in increasing both O3 and PAN. However the time of achieving the maximum of ozone value is retarded. When the initial concentration of NMHC and NOX increase, the yields of O3 and PAN are increased rapidly, the time of achieving the maximum of ozone concentration is postponed. from the simulation of CO, it can be seen that the yield of CO relates to the initial concentrations of NMHC and NOx, and CO level depends on the levels of NMHC and NOx, but do not have a simple linear relation between them. 3.The contour of ozone and PAN concentrations is plotted by using the Empirical Kinetics Modeling Approach(EKMA). The results reveal that the relationships between the maximum and formed rate of O3 and the ratio of NMHC to NOX are not a linear. Using the ridged line of EKMA, the type of photochemical smog pollution in city can be classified into A and B. Finally the mitigation measures of photochemical smog pollution in different kinds of city are proposed.