The correct form of the Webb, Pearman and Leuning equation for eddy fluxes of trace gases in steady and non-steady state, horizontally homogeneous flows

The original density corrections proposed by Webb et al. [Webb EK, Pearman GI, Leuning R (1980) Quart J Roy Meteorol Soc 106:85-100] for calculating the eddy fluxes of trace gases are shown to be correct for both steady and non-steady state, horizontally homogeneous flows. The revised theory replaces the original assumption of zero vertical flux of dry air with the requirement of no sources or sinks of dry air in the layer below the height of measurement.