This paper is concerned with the relationship between the spectrum of vertical displacement associated with the mesoscale spectrum of quasi-horizontal motions in the atmosphere and the mesoscale spectra of scalar passive additives. This work is based on observations of mesoscale atmospheric wave number spectra of wind, temperature, and certain trace species sampled in the altitude range 9--14 km by commercial aircraft during the Global Atmospheric Sampling Program (GASP). The principal result is that the scalar spectra are reasonably consistent with a simple model in which scalar fluctuations are produced by quasi two-dimensional motions acting in a plane inclined slightly to isentropic surfaces and to the isopleths of constant mixing ratio of trace species.