Key reactions in the photochemistry of hydrocarbons in Neptune's stratosphere

We studied the propagation of uncertainties carried by the reaction rate coefficients in the photochemistry of Neptune's stratosphere. We showed that the uncertainties on the mole fractions of main hydrocarbons are equal to or larger than the estimated uncertainties on abundances gathered from observations. From a global sensitivity analysis study, we determined a list of 26 key reactions and discussed the 7 main key reactions that should be studied in priority to lower the uncertainties in the mole fractions computed from a photochemical model. This methodology is essential to improve the predictivity of photochemical models and, consequently, to better understand the physical and chemical processes that govern the composition of giant planet atmospheres.