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A detailed study of ethane and ethylene photochemistry is presented for the troposphere and stratosphere. It is demonstrated that the loss of ethane is controlled by OH in the troposphere and Cl in the stratosphere. Observations of ethane show a stratospheric behavior indicative of a free chlorine concentration below 30 km that is only 10% of the predicted value given by both our photochemical model calculations and those done by others. The inferred lower amount of chlorine cannot be explained by heterogeneous processes for concentrations of aerosols representing average background conditions, nor does current stratospheric photochemistry show agreement. Chemical destruction of ethane and ethylene within the atmosphere leads to the production of carbon monoxide, formaldehyde, and other products. Tropospheric concentrations of formaldehyde are enhanced by nearly a factor of 3 for an ethylene mixing ratio of 2 ppb. Simultaneous monitoring of formaldehyde and carbon monoxide, as well as other products, will greatly aid in determining the relative importance of different tropospheric CO sources. Peroxyacetyl nitrate (PAN) acts as a reservoir for odd‐nitrogen at the expense of HNO 3 , HO 2 NO 2 , NO, and NO 2 .
Aikin et al. (Tue,) studied this question.