Atmospheric Chemistry Of Three Typical Chlorinated Alkenes

Chlorinated alkenes are significant chlorinated volatile organic compounds with abundant species.They are widely used as solvent,insecticide,and pharmaceutical intermediates.Chlorinated alkenes in the atmosphere,commonly emitted from anthropogenic activities,may damage human health upon contact exposure.Due to the carbon carbon double bond in the structure of chlorinated alkenes,they are highly active.Once they are emitted in the atmospheric environment,they can react with the main atmospheric oxidants(O3 molecular,OH radical,NO3 radical and Cl atom),which determines the fate of chlorinated alkenes in the atmospheric environment,and produce a series of secondary organic pollutants.To investigate the oxidation reactions of chlorinated alkenes in the atmosphere,the kinetic study on three typical chlorinated alkenes(3-chloro-2-methyl-l-propene,CMP;2,3-dichloropropene,DCP;3,4-dichlorobutene,DCB)reactions with O3 molecule,OH radical,NO3 radical and Cl atom at(298 ± 1)K and atmospheric pressure employing smog chamber system is reported.Furthermore,the most hazardous of the three typical chlorinated alkenes,CMP,is selected for study its reaction products and mechanisms with O3 molecule,OH radical,NO3 radical and Cl atom.All experiments were conducted in a 100 L Teflon reactor in a smog chamber system.Kinetics for the gas phase reactions of the three typical chlorinated alkenes with O3,were determined employing the absolute method and using an ozone analyzer to monitor the time resolution ozone concentration,kCMP+O3=(3.03±0.15)×10-18,kDCP+O3=(4.62±1.41)x1020,kDCB+O3=(2.09±0.24)×10-19.Kinetics for the gas phase reactions of the three typical chlorinated alkenes with OH radical,NO3 radical and Cl atom were determined employing the relative method and using a gas chromatography with a flame ionization detector(GC-FID)to monitor the concentration of organic compounds in the reactor.Rate constants obtained of OH reactions with three typical chlorinated alkenes were kCMP+OH=(3.83±0.21)×10-11,kDCP+OH=(1.37±0.07)x10-11 and?kDCB+OH=(1.45±0.08)×10-11.Rate constants obtained of NO3 reactions with three typical chlorinated alkenes were kCMP+NO3?(1.99±0.08)×10-14,kDCP+NO3=(1.45±0.08)×10-15 and kDCB+NO3?(3.00±0.25)×10-16.Rate constants obtained of Cl reactions with three typical chlorinated alkenes were kCMO+Cl=(2.40 ± 0.16)× 10-10,kDCO+Cl=(1.30±0.09)×10-10 and kDCB+Cl=(1.91±0.13)×10-10(all units in cm3 molecule-1 s-1).Main products of CMP reactions with O3 molecule,OH radical,NO3 radical and Cl atom were detected by a gas chromatography-mass spectrometer(GC-MS),and possible reaction mechanisms of their formation were proposed.Chloroacetone and formaldehyde were found to be the major products in all of the four oxidation reactions.The calculated atmospheric lifetimes of CMP,DCP and DCB based on the different oxidation rate constants reveal that the loss process of these three chlorinated alkenes and atmospheric implications of these reactions are discussed.Also,atmospheric implications of CMP oxidations products are discussed.