| Air pollution in China is characterized by local pollution gas concentration on the high side, dust weather, which led to the coexistence of trace gases and particles in the atmosphere. In our country, because of gaseous pollutants coming from coal, motor vehicle exhaust and industrial waste gases, etc., SO2, NO2 and C3H6 gases for the experimental research, and the typical oxides for particulate matter, such as titanium oxide, alumina and iron oxide were selected by using in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) to simulate approximate actual reaction processes of the atmosphere, coupled with ion chromatography and other testing means, to reveal the possible reaction mechanism.Firstly, heterogeneous reaction processes of pollution gases for 200 ppm were studied. As a result, under the dark reactions, the reactions of SO2 on surfaces either titanium oxide or alumina oxide, were both very weak, which there was only a small amount of sulfite generated. While NO2 joined, there was an obvious generation for sulfate, and this is because of different adsorption sites on the surface of the oxides. At the same time, there is a synergistic effect that the generating intermediate N2O4 promotesthe oxidation of SO2 to sulfate. It shows the less influence on the formation of sulfate as propylene joined in. But when NO2 and C3H6 entered into the system at the same time, the amount of generated sulfate is less than the amount of the reaction of SO2 with NO2. This indicated C3H6 inhibited the formation of sulfate, because C3H6has certain adsorption and reaction when introduced into the surface particle with no light on whose adsorption sites are similar to SO2, namely, the surface hydroxyl. For nitrate, it can be generated so long as NO2 was introduced into the system on the surface oxide. After SO2 appeared at the same time to join in the reaction, nitrate generated is sharply reduced, and that is because nitrates on the oxide surface mainly exist in water soluble state, which requires to bound water molecules, thus resulting in a competition with SO2 for water was taken part in the generation of sulfur species. After propylene added, little influence on the nitrate generated on the surface of titanium oxide, and inhibition effect on the alumina oxide can be observed, and the reason is the same as sulfate competing in surface hydroxyl. When both SO2 and C3H6 entered in the system, the amount of nitrate is least all of processes for inhibition strengthened.Under light illumination, on the surface of titanium oxide the most amount of sulfate is produced from the reaction of SO2 alone and the other processes all have inhibitory effects on sulfate generated. This is because the different reaction mechanisms between light and dark that NO2 and SO2 compete in surface hydroxyl adsorption sites, while SO2 and C3H6 compete with ROS radicals, resulting in sulfate decreased. In other oxide surfaces, NO2 can still promote the formation of sulfate, and this is because the activity of light of alumina and iron oxide is less than titanium oxide. As to nitrate, as long as the appearance of SO2, nitrate is reduced, and the principle is the same as under the dark reaction for the competition in the surface adsorption of water. And even when light on, nitrate is less than the amount in dark reaction of generation, and this is because water is not only involved in the NO2 and SO2 adsorption reaction for the various salts, but in light it will happen that the decomposition of nitrate to generate hydroxyl radicals and other species.Then,200 ppb concentration of gases are studied under the reaction processes, and on the surface of titanium oxide and light conditions sufate formed in the low concentration and high concentration is compared. It is found that two different concentrations have similar results for sulfate produced. When the reactions were proceeded with the condition of light, SO2 individually generated the most amount of sulfate, while both NO2 and C3H6 could inhibit the generation of sulfate. And the reaction mechanisms are the same as high concentration. It means that it is a very important and feasible method for laboratory studies to figure out the atmospheric chemical reaction rules in actual atmosphere. |
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