Effects of nonmethane hydrocarbons in the atmosphere

The photochemistry of several unreactive and moderately reactive nonmethane hydrocarbons (NMHC) in the background troposphere and stratosphere was investigated. A one‐dimensional steady state model was employed to determine the vertical distributions of C 2 H 6 , C 2 H 2 , C 3 H 8 , C 4 H 10 , and C 5 H 12 . The impact of these species upon the tropospheric and stratospheric odd‐hydrogen, odd‐oxygen, chlorine, and carbon systems was studied for various possible free radical profiles and eddy diffusion coefficients. Our results indicate that NMHC probably have only a small effect upon the background atmospheric photochemistry, although they might constitute a nonnegligible source of atmospheric CO. Also, Cl atoms, in predicted present‐day concentrations, comprise the major sink for stratospheric NMHC. Finally, if the chlorovinyl molecule (CHCl = CH) were stable in the lower stratosphere, it would then be conceivable that C 2 H 2 could be partially effective as a chain terminator to impede catalytic removal of stratospheric O 3 by Cl and ClO.