The Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) included channels centered at 6.9 μm (1370 cm-1 to 1560 cm-1) and 6.2 μm (1560 cm-1 to 1630 cm-1) to measure H2O and NO2, respectively. Since the photochemical lifetime of H2O is several months, no diurnal variation was expected, but retrieved concentrations at mid and low latitudes were larger in the daytime than in the nighttime (by 20--30% at 1 mbar). This is attributed to departure from local thermodynamic equilibrium of daytime emission which had not been accounted for in retrievals. It is shown that excess radiance in the lower mesosphere may be due to emission from the H2O(020)→(010) hot band and that in the stratosphere pumping of high vibrational states of NO2(&ngr;3) by chemical reaction NO+O3→NO2+O2 and by absorption of visible and near-IR sunlight may be the cause. This nonthermal emission from NO2 is shown to also significantly affect retrieval of H2O in the polar night mesosphere and NO2 in the daytime stratosphere at low latitudes. LIMS nighttime measurements of H2O and NO2 in regions other than the high latitude winter mesosphere should not be affected. ¿ American Geophysical Union 1989