A two-dimensional electrodynamic model is developed from first principles to study the microscopic physics of gas breakdown and charge transport in corona devices. The model uses a combination of particle simulation for atomic processes and macroscopic rate equations for the various chemical reactions. The particle model alternates between field solve and particle push. A Monte Carlo collision model is used to describe energy-dependent electron-neutral collisions including elastic collisions as well as ionization and dissociation processes. A novel “particle clumping” technique is introduced in phase space to create superparticles, thus restricting the total number of simulation particles to within a tractable number of a few million. It is shown that the model may be useful for studying microscopic air ionization physics, including the production of ozone. Some preliminary results are presented for both positive and negative DC corona devices.