The reaction Cl + H 2 CO→ HCl + HCO: Decreased sensitivity of stratospheric ozone to chlorine perturbations

The absolute rate constant for the reaction Cl + H 2 CO → HCl + HCO has been determined by the flash‐photolysis‐resonance fluorescence method to be 7.5 ± 0.9 (2σ) × 10 −11 cm³ molecule −1 sec −1 at 298K and to have a negligible temperature dependence. This rate which at stratospheric temperatures is more than 2000 times faster than the rate of Cl + CH 4 and more than a factor of 2 faster than Cl + HO 2 , indicates that formaldehyde (H 2 CO) will compete significantly with methane (CH 4 ) and HO 2 for the conversion of active chlorine in the stratosphere to the inactive reservoir HCl. Chlorine will thus be a less efficient destroyer of stratospheric ozone than previously believed. One‐dimensional eddy‐diffusion photochemical model calculations indicate that the eventual ozone depletion for a steady‐state CFM release at 1975 rates (750,000 tons/year) will be lowered from 20% to 18.5% by the inclusion of this reaction.