Experimental study of the mesospheric removal of NF3 by neutral meteoric metals and Lyman-α radiation.

NF3 is a potent anthropogenic greenhouse gas with increasing industrial usage. It is characterized by a large global warming potential due in part to its large atmospheric lifetime. The estimated lifetime of about 550 years means that potential mesospheric destruction processes of NF3 should also be considered. The reactions of NF3 with the neutral metal atoms Na, K, Mg and Fe, which are produced by meteoric ablation in the upper mesosphere, were therefore studied. The observed non-Arrhenius temperature dependences of the reactions between about 190 and 800 K are interpreted using quantum chemistry calculations of the relevant potential energy surfaces. The NF3 absorption cross section at the prominent Lyman-α solar emission line (121.6 nm) was determined to be (1.59 ± 0.10) × 10(-18) cm(2) molecule(-1) (at 300 K). In the mesosphere above 60 km, Lyman-α photolysis is the dominant removal process of NF3; the reactions with K and Na are 1-2 orders of magnitude slower. However, the atmospheric lifetime of NF3 is largely controlled by reaction with O((1)D) and photolysis at wavelengths shorter than 190 nm; these processes dominate below 60 km.