Chemical And Photochemical Transformation Of Some Organic Pollutants In The Atmosphere

There are many volatile organic compounds (VOCs) and semi-volatile organic compounds (SOCs) existed in atmosphere, they can be transformed by chemical processes or photolychemical processes in environment. Photolysis is an important transformation for polycyclic aromatic hydrocarbons (PAHs) and other SOVs in the atmosphere. There have been many researches about the photodegradation of PAHs in aquatic solution and on particulate, but few researches reported the photolytic behavior on the surface of vegetation. In order to discuss the role of plants on the photochemical behavior of PAHs, the photodegradation of the 16 PAHs sorbed on pine needles was investigated in this research.Pine (Finns tabulaeformis Carr.) needles were exposed to the exhaust gas containing PAHs generated by combustion of polystyrene and wood in stove. And the PAHs were accumulated in the wax of pine needles to a certain concentration. Under the irradiation of sunlight and UV, the photochemical behaviors of PAHs on pine needles were studied.The pine needles fortified with 16 EPA-PAHs were exposed to sunlight irradiation at atmospheric conditions, and the photodegradation of PAHs follows the first-order reaction kinetics. The photolytic half-life of PAHs ranges from 12.5h to 65.4 h. Though longer than the half-life of PAHs in aquatic solution, it is much shorter than the half-life of particle-bound PAHs. It is concluded that vegeatation is an important fate of PAHs in nature.With the irradiation of UV, the photolysis of PAHs dissolved in the extracted cuticular wax was investigated. The findings of this study suggest the processing which consists of two phases: within the first 20 h the photodegradation follows pseudo-first-order kinetics, within a longer observation period, the first phase seems to proceed to a second phase with retarded decomposition of the PAHs. The photolytic half-life of PAHs was determined about 5h to 13h, shorter than data got from live pine needles.In the troposphere, VOCs such as alkanes,alkenes, are transformed by the chemical process reaction with the hydroxyl radical ( OH). By the use of partial least squares (PLS) method, a linear free energy relationship model for rate constants of 51 alkanes and 76 alkenes reacting with the hydroxyl radical ( OH) in gas phase was developed. The model is surely stable and has a good prediction ability, and may be used to make predictions for the rate constants of other alkanes and alkenes reacted with OH.