Chlorine atom initiated reactions of selected tropospheric halocarbons-Kinetic and product studies

摘要

Halogens are suggested as important atmospheric oxidants in the marine boundary layer.The room-temperature kinetics of the chlorine-initiated reactions of three biogenic brominated hydrocarbons and four anthropogenic chlorinated ethenes was investigated by gas chromatography with flame ionization detection(GC-FID)at a pressure of 1 atm(1 atm=101.325 kPa)in air,using the relative rate technique.The rate constants(x 10~(13)cm3 molecule~(-1)s~(-1))for CH2Br2,CHBr2Cl,and CHBr3 reactions at 298 + 2 K were found to be 4.25 +-0.65,2.03 + 0.31,and 2.81 +-0.41,respectively,using methane as a reference compound.Room temperature rate constants(+-10~(1l)cm3 molecule~(-1)s~(-1))obtained for 1,1-dichloroethene,cis-dichloroethene,trans-dichloroethene,and trichloroethene using ethene as a reference are 13.4 +-3.3,9.1 +-2.3,7.4 +-1.8,and 7.7 +-1.9,respectively.The rate constants of chlorine-atom reactions with various hydrocarbons obtained in this work and taken from literature were correlated with corresponding rate constants of the OH radical available in the literature.The temperature dependences for the reactions of chlorine atoms with chlorinated ethenes were studied within the 298-358 K range.The corresponding Arrhenius expressions for the rate constants are(cm3 molecule~(-1)s~(-1)):In k=(-25.26 +-0.17)-(758 +-55)/T for 1,1-dichloroethene,1n k=(-25.79 +-0.10)-(799 +-34)/T for cis-dichloroethene,In k=(-26.74 +-0.09)-(1018 +-28)/T for trans-dichloroethene,and 1n k=(-26.10 +-0.26)-(846 +-83)/T for trichloroethene.In addition,product studies for the chlorine-initiated gas phase oxidation reactions of CHBr3 and CHBr2Cl were performed using gas chromatography with mass spectrometric detection(GC-MS).The only identified product for the reaction of CHBr3 with Cl reaction was COBr2,while for the CHBr2Cl + Cl reaction,COBrCl and COCl2 were observed,indicating the possibility of halogen atom release.The atmospheric implications of the results obtained are discussed.