MALTA: A zonally averaged global atmospheric transport model for long-lived trace gases

We present a two-dimensional, zonally averaged global model of atmospheric transport named MALTA: Model of Averaged in Longitude Transport in the Atmosphere. It aims to be accessible to a broad community of users, with the primary function of quantifying emissions of greenhouse gases and ozone depleting substances. The model transport is derived from meteorological reanalysis data and flux-gradient experiments using a three-dimensional transport model. Atmospheric sinks are prescribed loss frequency fields. The zonally averaged model simulates important large-scale transport features such as the influence on trace gas concentrations of the quasi-biennial oscillation and variations in inter-hemispheric transport rates. Stratosphere-troposphere exchange is comparable to a three-dimensional model and inter-hemispheric transport is faster by up to 0.3 years than typical transport times of three-dimensional models, depending on the metric used. Validation of the model shows that it can estimate emissions of CFC-11 from an incorrect a priori emissions field well using three-dimensional (3D) mole fraction fields generated using a different 3D model than which the flux gradient relationships were derived. The model is open source and is expected to be applicable to a wide range of studies requiring a fast, simple model of atmospheric transport and chemical processes for estimating associated emissions or mole fractions.