An equation for analyzing the kinetic results for the droplet-train apparatus with a wall loss is derived. We show that the presence of a radial concentration gradient due to loss on the flow reactor wall significantly affects the measured uptake coefficient gamma(meas) on droplets in the center of the reactor. For an efficient wall loss gamma(meas) can be similar to60% less than that calculated without consideration of the loss on the wall. This revision of the kinetics for species with a wall loss leads to an increase in the uncertainty of the extracted gas-surface reaction probability for high water vapor pressure experimental conditions.