Global sensitivity of aviation NO x effects to the HNO 3-forming channel of the HO 2 + NO reaction
The impact of a recently proposed HNO
3-forming channel of the HO
2 + NO reaction on atmospheric ozone, methane and their precursors is assessed with the aim to investigate its effects on aviation NO
x induced radiative forcing.
The first part of the study addresses the differences in stratospheric and tropospheric HO x-NO x chemistry in general, by comparing a global climate simulation without the above reaction to two simulations with different rate coefficient parameterizations for HO 2 + NO → HNO 3. 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 NO x effects are isolated independently for each of the three above simulations. Warming and cooling effects of aircraft NO x emissions are both enhanced when considering the HNO 3-forming channel, but the sum is shifted towards negative radiative forcing. Uncertainties associated with the inclusion of the HO 2 + NO → HNO 3 reaction and with its corresponding rate coefficient propagate a considerable additional uncertainty on estimates of the climate impact of aviation and on NO x-related mitigation strategies.