In this paper, the question of what happens when an air parcel in which photochemical processes take place moves around the earth with a certain velocity is considered. When the characteristic chemical system time corresponds to the rotation period of the earth (1 day) an in uence of the diurnal variation of the chemical constituents on the zonal wind is found. We term this ΓΏnding the zonal wind e ect on the photochemistry (ZWEPC). The period of forcing of the chemical system within the air parcel changes depending on the direction and strength of the zonal wind. The alteration of the respective frequency has been described by a modiΓΏed Doppler formula. A remarkable in uence of the zonal wind on the photochemistry was found in the upper mesosphere=mesopause region where the characteristic chemical system time ranges in the order of one day and the system represents a nonlinear chemical oscillator which is able to create nonlinear e ects such as subharmonics. The zonal wind in uences such magnitudes as the occurring time of the daytime ozone maximum or the diurnal amplitude of atomic hydrogen and others. As the zonal wind changes with season the ZWEPC has to be taken into consideration when interpreting observations.