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.