This article demonstrates quantitatively how far reactions are from chemical equilibrium over the full space of a two-dimensional atmospheric model. This method could be used with data where an instrument-equipped aircraft measures numerous species simultaneously, An atmospheric reaction is displaced from equilibrium by solar radiation and relocation of species by atmospheric motions, One purpose of this study is to seek additional stratospheric or tropospheric gas-phase chemical reactions that might undergo heterogeneous catalysis. Hypothetical cases can be rapidly screened in terms of their thermodynamic potential to react under measured or modeled atmospheric conditions of temperature and local species concentrations. If a reaction is interesting, is slow in the gas phase, and has a high thermodynamic tendency to react, it is a good candidate for a laboratory study to seek a heterogeneous catalyst, if the reaction is thermodynamically unfavorable, there is no catalyst that can cause the reaction to occur. If a reaction is thermodynamically favored to occur but also endothermic, it will tend to be slow at stratospheric temperatures. We find, as expected, that four heterogeneous reactions important in causing the Antarctic ''ozone hole'' have high thermodynamic tendencies to occur under atmospheric conditions, but one of these is only weakly thermodynamically allowed in some regions of the atmosphere. The reaction of SO2 and HNO3 to form HONO has a high thermodynamic potential to occur, is a well-known laboratory reaction at ice temperature, and may occur in nitric acid-rich sulfate aerosols. Throughout the troposphere and stratosphere, we find that formaldehyde has an extremely high thermodynamic potential to reduce. nitric acid. Formaldehyde is known to stick to and remain in sulfuric acid solution, where it adds water to form H2C(OH)(2). Near room-temperature H2C(OH)(2) reacts with nitric acid in a two-step mechanism to form two molecules of HONO, but the rate of this process under conditions of stratospheric sulfuric acid aerosols is unknown.