Nonlocal thermodynamic equilibrium effects in stratospheric HF by collisional energy transfer from electronically excited O(2) and implications for infrared remote sensing

A possible nonlocal thermodynamic equilibrium (non-LTE) effect involving stratospheric HF arising from the direct photochemical excitation of vibrationally excited HF by collisional energy transfer from electronically excited O(2) [O(2)((1)Delta), O(2)((1)Sigma)] is presented. Although this non-LTE effect is smaller than one associated with the direct solar excitation of both HF(nu= 1) and HF(nu= 2), calculations show that inclusion of the mechanism proposed here into retrieval algorithms is necessary if correct daytime upper stratosphere HF profiles are to be inferred in future infrared thermal emission measurements. Accurate determinations of the state-to-state rate constants of the reactions involved in these excitation processes and of the quenching rates of vibrationally excited HF are needed if IR thermal emission techniques are to be accurately employed in the measurement of stratospheric HF.

Nonlocal thermodynamic equilibrium effects in stratospheric NO and implications for infrared remote sensing

It is shown that the vibrational state population of stratospheric nitric oxide (NO) could be substantially different from that expected on the basis of local thermodynamic equilibrium (LTE). Deviations from LTE may arise because stratospheric NO can be photochemically produced from NO(2) with several vibrational quanta. Model calculations suggest that the population of NO(upsilon = l) could be some 30% above that expected from LTE at 30 km with smaller enhancements above and below. Substantially larger enhancements are predicted for NO(upsilon = 2). This result is shown to have important implications for NO determination by remote sensing of IR emission. Data needed for the quantification of these effects are enumerated.