Uptake of formaldehyde by sulfuric acid solutions: Impact on stratospheric ozone

Chemical reactions on sulfuric acid aerosols have recently been shown to play an important role in stratospheric chemistry. In particular, these reactions push odd‐nitrogen compounds into HNO 3 and thereby enhance the chlorine‐catalyzed destruction of ozone. It has been suggested that our current set of heterogeneous reactions may be incomplete. Indeed we show that formaldehyde, CH 2 O, is rapidly and irreversibly taken up by stirred sulfuric acid solutions (60 to 75 wt % H 2 SO 4 at −40° to −65°C) with uptake coefficients as large as γ = 0.08. If similar uptake occurs under stratospheric pressures of CH 2 O (that is, 1000 times lower than used in the present study), then the removal of CH 2 O from the gas phase can take away a significant source of odd hydrogen in the mid‐ and high‐latitude lower stratosphere. We show here that with the inclusion of this reaction, concentrations of OH and HO 2 are reduced by as much as 4% under background levels of aerosols and more than 15% under elevated (volcanic) conditions. Further, the accumulation of CH 2 O in stratospheric aerosols over a season may alter the composition and reactivity of these sulfuric acid‐water mixtures.