Nonlocal thermodynamic equilibrium vibrational, rotational, and spin state distribution of NO(ν = 0, 1, 2) under quiescent atmospheric conditions

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Abstract
A nonlocal thermodynamic equilibrium (non‐LTE) model for the NO(ν ≤ 2, J, S) state distributions for altitudes from ground to 200 km for nonauroral conditions is presented. The model includes (1) vibrational excitation due to collisions of NO with O and O2, (2) excitation due to photolysis of NO2 and due to NO2 + O→ NO + O2 in the stratosphere, and (3) excitation due to N(4S,2 D) +O2 → NO + O in the thermosphere. Spontaneous emission, induced emission, and absorption of tropospheric and solar radiation are included. Intravibrational spin and rotational relaxations are included by means of an exponential power gap law approach. This model improves upon previous work mainly through its completeness. It provides non‐LTE distributions of the three spin, rotational, and vibrational degrees of freedom covering the whole atmosphere up to the upper thermosphere. All previous knowledge of non‐LTE excitation processes of NO has been incorporated. The most important results of the model are (1) the stratospheric daytime vibrational distribution departs from local thermodynamic equilibrium (LTE) due to NO(ν≥1) production by NO2 photolysis; (2) the rotational and spin distributions of the NO(ν = 1, 2) are in non‐LTE above ∼110 km; (3) a 90% propensity to conserve the spin orbit state in intravibrational NO+O collisional relaxation was determined by comparison of the model results to cryogenic infrared radiance for shuttle (CIRRIS‐1A) data. The implications of the non‐LTE model results to remote sensing of stratospheric NO abundances from spectrally resolved 5.3 μm limb radiances are discussed. The neglect of thermospheric rotational/spin non‐LTE as well as the neglect of NO(ν>1) production by NO2 photolysis map into errors in the modeled spectra of 20–25%.

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