We use in situ observations of H₂O₂ to study the interplay between photochemistry, transport and deposition processes. The data were obtained during five ground-based field campaigns across Europe. A budget calculation indicates that the photochemical production rate was much larger than photochemical loss and that dry deposition is the dominant loss process. To reproduce the change in H₂O₂ mixing ratios after sunrise, a variable contribution of entrainment from the residual layer is required.