We have investigated the plasma processes in an atmospheric pressure glow discharge (APGD) in He used for analytical spectrometry, by means of fluid and Monte Carlo (MC) simulations. Typical results include the potential and electric field distributions in the plasma, the density profiles of the various plasma species throughout the discharge, the mean electron energy, as well as the rates of the various collision processes in the plasma, and the relative importance of the different production and loss rates for the various species. The similarities and differences with low pressure glow discharges are discussed. The main differences are a very small cathode dark space region and a large positive column, as well as the dominant role of molecular ions. Some characteristic features of the APGD, such as the occurrence of the different spatial zones in the discharge, are illustrated, with links to experimental observations.