Abstract
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 HNO3 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, CH2O, is rapidly and irreversibly taken up by stirred sulfuric acid solutions (60 to 75 wt % H2SO4 at −40° to −65°C) with uptake coefficients as large as γ = 0.08. If similar uptake occurs under stratospheric pressures of CH2O (that is, 1000 times lower than used in the present study), then the removal of CH2O 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 HO2 are reduced by as much as 4% under background levels of aerosols and more than 15% under elevated (volcanic) conditions. Further, the accumulation of CH2O in stratospheric aerosols over a season may alter the composition and reactivity of these sulfuric acid‐water mixtures.
Highlights
In the past severalyears, laboratory,field, and modeling studies have provided mounting evidence that heterogeneous reactions on naturally occurring stratosphericaerosolscould be impacting ozone on a global scale
For the experimentin formaldehydepolymerization is known to occur at high Ctt20 Figurela weaddeda totalof approximate7lyx1016moleculeosf pressureasndlow temperatures[Walker,1964],thehigherpressure CH20 to our 20 ml solution of sulfuric acid in 600 s
The uptakeefficiencieswe obtainfor CH20 on stixred60 to Althoughwe alwaysobservedsignificantCH20 uptakeon 75 wt % H2SO4 solutionsas a functionof temperatureare givenin sulfuric acid whether or not we stirred the solution, we found that Figure2
Summary
Laboratory,field, and modeling studies have provided mounting evidence that heterogeneous reactions on naturally occurring stratosphericaerosolscould be impacting ozone on a global scale. Laboratory measurements[Mozurkewich and Calvert, 1988; Tolbert et al, 1988; Van Doren et al, 1991; Hanson and Ravishankara, 1991a] have shown that reactions (1) and (2) occur on sulfuric acid solutionsthoughtto be representativeof the stratosphericsulfate layer. We use a photochemical model to demonstrate the first-order atmospheric impact of heterogeneousuptake of formaldehyde by sulfuric acid aerosols. The CH20 density and the sulfuric acid volume.
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