The Impact Of Vehicle Exhausts On Photochemical Smog In City

Photochemical Smog is one of the most harmful pollutions to urban atmosphere. It is a new air pollution phenomenon appearing after petrol as fuel. The essence of photochemical smog is ozone pollution which is formed by nitrogen oxides and hydrocarbons under ultraviolet ray radiation. In urban atmospheric environment, the main sources of NO_x and HC are vehicle exhausts. More than 40% NO_x, 80% CO and 70% HC come from the vehicle exhausts in large cities respectively. Photochemical smog caused by vehicle exhausts has received a considerable research interest.In the last 20 years, the amounts of vehicles have increased dramatically, and also they mainly concentrate on large cities, so the air pollution problems in large cities are more and more serious. In order to understand the impact of exhausts on photochemical fog, this paper summarizes the present conditions and trends of exhaust pollution, then discusses photochemical smog formation mechanism, establishes the photochemistry dynamics system of equations and carries on the mathematical simulation to them, finally proposes the mitigation measures of city photochemical smog pollution. The conclusions are summarized as follows:1. The urban air pollution of our country is being transformed to the exhaust type of motor vehicle (photochemical smog type) from the soot type. Since 1990, the average annul growth rate of vehicle amounts of Beijing, Shanghai and Guangzhou are 12.03%, 14.82% and 9.75% respectively. The vehicle exhausts have already been primary pollution sources of Beijing, Shanghai and Guangzhou. The sharing rates ofBeijing are——CO 80.3%, HC 79.1% and NO_x 54.8%; Shanghai are——CO61.8%, HC 56.7% and NO_x 20.9%; Guangzhou are——CO 86.8%, HC 97.4% andNO_x 26.0%.2. The meteorological conditions that can stimulate the emergence ofphotochemical smog are——sun radiation intensity large, wind speed low,atmosphere spread condition poor, inversion phenomena, etc.3. The photochemical smog formation mechanism contains 12 essential reactions. The primary pollutants participating in these reactions are NO₂, NO, RH and RCHO. These primary pollutants mainly come from vehicle exhausts in urban...