EVo calculates the speciation and volume of a volcanic gas phase erupting in equilibrium with its parent magma. Models can be run to calculate the gas phase in equilibrium with a melt at a single pressure, or the melt can be decompressed from depth rising to the surface as a closed-system case. Single pressure and decompression can be run for OH, COH, SOH, COHS and COHSN systems. EVo can calculate gas phase weight and volume fraction within the system, gas phase speciation as mole fraction or weight fraction across numerous compounds, and the volatile content of the melt at each pressure. It also calculates melt density, f02 of the system, and more. EVo can be set up using either melt volatile contents, or for a set amount of atomic volatile which is preferable for conducting experiments over a wide range of fO2 values.

EVolve calculates the chemical composition and surface pressure of a ID atmosphere on a rocky planet that is being produced by volcanic activity, as it grows over time. Once the initial volatile content of the planet's mantle and the composition and resultant surface pressure of any pre-existing atmosphere is set, the volcanic degassing model EVo (ascl:2307.052) calculates the amount and speciation of any volcanic gases released into the atmosphere over each time step. Atmospheric processing is calculated using FastChem (ascl:1804.025); thermochemical equilibrium is assumed so the final chemical composition of the atmosphere is calculated according to the pre-set surface temperature.