Is quenching of electronically excited NO2 by N2 an important atmospheric source of N2O?

Context Abstract: The atmospheric budget of N₂O, a greenhouse gas and the dominant source of total reactive nitrogen to the stratosphere, remains a controversial subject. Gas-phase atmospheric chemical sources of N₂O are not well documented, but studies of atmospheric N₂O samples show a mass-independent heavy oxygen isotope enrichment which is suggestive of the existence of missing in situ sources or sinks. We have studied N₂O production from the reaction of electronically excited NO₂ with N₂. Contrary to earlier findings, our results show that this process is an insignificant source of atmospheric N₂O.

Main Abstract: Production of N₂O as a product of the collisional deactivation of electronically excited NO₂ by N₂ has been investigated with the goal of establishing the importance of this process in the atmospheric N₂O budget. The experimental approach minimizes potential interferences from heterogeneous reactions, multiphoton processes, and self-quenching. At the 95% confidence limit, we find that the quantum yield for production of N₂O from 488 nm photolysis of 60 Torr of 0.1% NO₂ in N₂ is less than 4 × 10⁻⁸, i.e., at least 10,000 times smaller than a previously published value; this result suggests that quenching of electronically excited NO₂ by N₂ is unimportant as a source of atmospheric N₂O.