Studies On Reactions Of Nitric Oxides With Volatile Organic Compounds In Atmosphere

The atmospheric environmental pollution, especially the aerosol pollution has long been an elusive topic for scientists. It is very difficult to be resolved due to its features such as complexity of pollutant, variety of the influence factors, wide range, and difficulty of control etc. Among the aerosol, the secondary organic aerosol (SOA) is very important and most of them are PM2.5, which can pose grave threat to ecosystem and mankind because the SOA can not only cause atmospheric photochemical smog and acid deposition affecting visibility and regional climate, but also contain various highly toxic organic compounds. The SOA is the main contribution of the aerosol in global atmosphere. It can be formed by oxidation or photooxidation of biogenic and anthropogenic volatile organic compounds (BVOCs,AVOCs) in the atmospheric environment.In the first part of this thesis, some concepts, research background, the concerned developments as well as the research significance and novelty of this work have been described here. The aerosol, SOA and its generation mechanism as well as the VOCs including its category, origin, and harms are also depicted in details. Although VOCs are only trace gas in the atmosphere, the studies on the VOCs play a great role in the field of atmospheric chemistry. Most of the VOCs are so active enough to be involved in a variety of chemical and photochemical reactions. As a result, the derivatives and products from VOCs thus affect many aspects such as the component of air, transformation of pollutant, regional atmospheric quality and change of regional climate. Therefore, the investigation on the atmospheric chemistry and photochemistry of VOCs has long been the research focus of scientists. It is well known that the isoprene is the most important BVOCs in air. Recent studies show that the epoxide is the key intermediate in the process of SOA formation from isoprene. It is believed that the formation of epoxide is very important to investigate the mechanism for the SOA formation via isoprene. Hence, the research on the atmospheric chemistry and photochemistry of epoxide has become a new hotspot in the current field of atmospheric chemistry.In the secondary, the third and the fourth part of this thesis, the main experimental studies have been demonstrated in details. The mechanism for SOA formation via VOCs in air has been investigated extensively through a series of carefully designed experiments. Additionally, the chemical reactions of some precursors of SOA with nitric oxides in atmosphere have also been studied. The details for the corresponding experimental methods, procedures and the conclusions have been described as following.(1) Nine epoxides represented the typical derivatives of BVOCs have been prepared by using two different methods. The reactions of epoxides with nitrogen dioxide (NO2) in water, gas phase and organic phase have been carried out respectively. In addition, the reaction kinetics and mechanism have also been investigated extensively. The results indicate that the corresponding organic nitrates have been obtained by the reactions of epoxides with NO2in water, gas phase and organic medium, and the organic nitrates have been proved to be component of SOA. As a result, these experiments find a novel possible process of SOA formation from epoxide. The results also suggest that organic nitrates in atmosphere can be formed directly by reactions of epoxides with NO2apart from reaction of epoxide with inorganic nitrate and nitric acid, which is well known before. In addition, the kinetics studies indicate that the reaction of epoxide with NO2can be considered as first order reaction under the conditions of high NO2concentration, and the linear fitting results also fit the first order kinetics curve well. Finally, the mechanistic studies suggest that the reaction of NO2with epoxide most likely proceeds via a free radical process.(2) The chemical and photochemical reactions of NO2with a large class of important AVOCs arenes derived from city atmospheric SOA have been carried out in this part. Eight representative arenes have been synthesized and the gas phase reactions of these compounds with NO2with and/or without light irradiation have also been investigated. All of the products have been determined by chromatography and the possible mechanism has also been studied. The results indicate that a series of nitrobenzenes have been formed by gas phase reactions of arenes with NO2under or not light irradiation. Therefore, a conclusion can be drawn out that the nitrobenzenes in air and environment are produced not only by anthropogenic emissions from chemical industry, but also by direct radical reaction of NO2with these volatile organic arenes.(3) In the fourth part, seven representative arenes have been prepared. Additionally, with or without light irradiation, the reactions of nitric oxide (NO) with these compounds in gas phase have been carried out. Furthermore, careful analysis of the results as well as the mechanism has also been done. Similarly, the results show that various nitrobenzenes have also been obtained by the gas phase reactions of NO with arenes under light irradiation or not, which confirm a new process of nitrobenzene formation in atmosphere and environment. This means that these hazardous nitrobenzene derivatives not only come from chemical industry emissions, but also can be generated by direct radical or single electron transfer reactions of NO with atmospheric volatile organic aromatic compounds.Finally, the author summarizes all of the experiments, methods, results and conclusions. In addition, the continuous work plan and blueprint in the future have also been drawn out at the end of this thesis.