The distribution of atmospheric methane concentrations downwind of a landfill was measured by a continuous measuring system equipped with a flame ionization detector. The observed data show dispersion of the methane plume entitled from the landfill. On the basis of an atmospheric diffusion model, the methane emission rate of 3--5¿108 g/day was estimated for this 2¿106 m2 landfill. ¿ American Geophysical Union 1993