The Mechanism And Kinetic Studies On The Reaction Of Hexachloro-1,3-butadiene And Benzoic Acid In The Atmosphere

Environmental issues are of great significance in the improvement of living standards,economic progress,and the development of the country.Scientific researchers have also paid more attention to air pollution research.Persistent organic pollutants and aromatic compounds have an impact on the formation of atmospheric secondary aerosols,photochemical reactions,the nature of clouds,and the ecological environment.The study of the reaction mechanism also has certain support for the control of industrial pollution emissions.The use of atmospheric free radicals and oxidants on the degradation of air pollution in a variety of scientific research and practical application has received widespread attention.In this paper,we choose hexachlorobutadiene in persistent organic pollutants and benzoic acid in aromatic acid as the research object,using a variety of free radicals and oxidants to study the reaction mechanism for OH,Cl,NO3,HO2 and O3 with hexachlorobutadiene,and OH,NO3,SO4-induce the oxidation degradation of benzoic acid.This study can provide data to the degradation of pollutants.Density functional theory was used in the calculation and the reaction mechanism were studied at the MPWB1K/6-31+G(d,p)levels and the 6-311+G(3df,2p)levels.The reaction rate constants were calculated by the transition state theory,then the relationship between the reaction rate constants,temperature and the height was given.The following conclusions are obtained:1.Mechanism and the kinetic studies of hexachlorobutadiene with Cl,NO3,HO2,OH and O3Those reactions are optimized and calculated at two carbon sites of double bonds,and all addition reactions are exothermic.The reaction barriers at the Ci site are smaller than the C2 site,and the reaction barriers of hexachlorobutadiene with Cl and OH is smaller,while the reaction barrier with HO2 and O3 is larger.The addition products of HCBD with Cl,NO3,HO2,OH can react with O2/NO,and the reaction barriers at C2 is higher than C1 site,while the reaction heat is opposite.Ozonization reactions of HCBD including the formation of primary and secondary ozonides are investigated.The criegee intermediates created in the ozonization reactions can react with O2,SO2,NO2 and H2O.The reaction rate constants of the Cl,NO3,HO2,OH and 03 at 298.15 K are 4.51x10-13,1.32×10-20;4.33X10-29,6 33×10-16 and 5.8×10-27 cm3·molecule-1·s-1 respectively.And the total reaction rate constant is 4.51×10-13 cm3·molecule-1·s-1.The reactions of OH and Cl radicals with HCBD are more important than those of NO3,HO2 and O3 according to the reaction rate branching ratio.The vertical structure of the atmosphere will cause the temperature changes with height,and according the the relationship of temperature,altitude and reaction rate,HCBD will be higher in concentrations at near the ground and the mountains than in other place.2.Mechanism and the kinetic studies of benzoic acid and OH,NO3 and SO4-The reaction mechanism of OH,NO3 and SO4-with benzoic acid in atmospheric water droplets,the initiation and subsequent reactions of benzoic acid with OH radicals in the gas phase were studied in this paper.In liquid phase,there are two pathways of OH wiht benzoic acid including the addition abstraction and abstraction addition reactions.In products,6-hydroxybenzoic acid and 4,6-dihydroxybenzoic acid were most stable,while the 3-hyhydroxybenzoic acid and 3,5-dihydroxybenzoic acid had relatively highest energy.The results showed that the potential barriers of the addition initiated reactions of benzoic acid with OH radical are lower than those of other abstraction initiated reactions.And as for the potential barriers of initiated reaction,the ortho-position reactions of OH are less than the meta-position and para-position reactions,while for NO3 and SO4-,the ortho-position reactions are more than the meta-position and para-position reactions.Overall,the potential barriers of OH-initiated reaction are less than NO3 and SO4-reactions.The initiation reactions of OH radical and benzoic acid are exothermic but the abstraction reactions of NO3 and SO4-are endothermic processes.In atmosphere,the products of addition and extraction of benzoic acid and OH radicals could be further oxidized by O2/NO.The total reaction rate constants of OH and at NO3 298.15 K in atmospheric water droplets are 3.35x10-15 cm3-molecule-1·s-1 and 1.12×10-26 cm3-molecule-1·s-1,respectively.There is a link between rate constants,temperature and altitude.