Abstract
The method of entrainment-limited kinetics enables atmospheric chemistry models that do not resolve clouds to simulate heterogeneous (surface and multiphase) cloud chemistry more accurately and efficiently than previous numerical methods. The method, which was previously described for reactions with first-order kinetics in clouds, incorporates cloud entrainment into the kinetic rate coefficient. This technical note shows how bimolecular reactions with second-order kinetics in clouds can also be treated with entrainment-limited kinetics, enabling efficient simulations of a wider range of cloud chemistry reactions. Accuracy is demonstrated using oxidation of SO2 to S(VI) – a key step in formation of acid rain – as an example. Over a large range of reaction rates, cloud fractions, and initial reactant concentrations, the numerical errors in the entrainment-limited bimolecular reaction rates are typically << 1 % and always < 4 %, which is far smaller than the errors found in several commonly used methods of simulating cloud chemistry with fractional cloud cover.
Highlights
20 Aqueous reactions in clouds play an important role in atmospheric chemistry, production of acid rain from SO2 being a prominent example (Seinfeld and Pandis, 2016)
This technical note shows how bimolecular reactions with second-order kinetics in clouds can be treated with entrainment-limited kinetics, enabling efficient simulations of a wider range of cloud chemistry reactions
3 Evaluation The accuracy of entrainment-limited bimolecular reaction rates will be demonstrated using oxidation of S(IV) by aqueous H2O2, which is a prominent step in the formation of S(VI) and acid rain, 85 as an example (Chameides, 1984)
Summary
20 Aqueous reactions in clouds play an important role in atmospheric chemistry, production of acid rain from SO2 being a prominent example (Seinfeld and Pandis, 2016). Over a large range of reaction rates, cloud fractions, and initial reactant concentrations, the numerical errors in the entrainment-limited bimolecular reaction rates are typically
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