Global sensitivity of aviation NOx effects to the HNO 3-forming channel of the HO2 + NO reaction

Abstract

The impact of a recently proposed HNO3-forming channel of the HOF2 + NO reaction on atmospheric ozone, methane and their precursors is assessed with the aim to investigate its effects on aviation NOx induced radiative forcing. The first part of the study addresses the differences in stratospheric and tropospheric HOx-NOFx chemistry in general, by comparing a global climate simulation without the above reaction to two simulations with different rate coefficient parameterizations for HOF 2 + NO → HNOF3. A possible enhancement of the reaction by humidity, as found by a laboratory study, particularly reduces the oxidation capacity of the atmosphere, increasing methane lifetime significantly. Since methane lifetime is an important parameter for determining global methane budgets, this might affect estimates of the anthropogenic greenhouse effect. In the second part aviation NOx effects are isolated independently for each of the three above simulations. Warming and cooling effects of aircraft NOx emissions are both enhanced when considering the HNO3-forming channel, butthe sum is shifted towards negative radiative forcing. Uncertainties associated with the inclusion of the HOF2 + NO !HNOF3 reaction and with its corresponding rate coefficient propagate a considerable additional uncertainty on estimates of the climate impact of aviation and on NOx-related mitigation strategies. © Author(s) 2013.