H2O2 and CH3OOH (MHP) in the Remote Atmosphere: 2. Physical and Chemical Controls

Hydrogen peroxide (H2O2) and methyl hydroperoxide (MHP, CH3OOH) serve as HOx (OH and HO2 radicals) reservoirs and therefore as useful tracers of HOx chemistry. Both hydroperoxides were measured during the 2016-2018 Atmospheric Tomography Mission as part of a global survey of the remote troposphere over the Pacific and Atlantic Ocean basins conducted using the NASA DC-8 aircraft. To assess the relative contributions of chemical and physical processes to the global hydroperoxide budget and their impact on atmospheric oxidation potential, we compare the observations with two models, a diurnal steady-state photochemical box model and the global chemical transport model Goddard Earth Observing System (GEOS)-Chem. We find that the models systematically under-predict H2O2 by 5%-20% and over-predict MHP by 40%-50% relative to measurements. In the marine boundary layer, over-predictions of H2O2 in a photochemical box model are used to estimate H2O2 boundary-layer mean deposition velocities of 1.0-1.32 cm s(-1), depending on season; this process contributes to up to 5%-10% of HOx loss in this region. In the upper troposphere and lower stratosphere, MHP is under-predicted and H2O2 is over-predicted by a factor of 2-3 on average. The differences between the observations and predictions are associated with recent convection: MHP is under-estimated and H2O2 is over-estimated in air parcels that have experienced recent convective influence.