Fundamental oxidation processes in the remote marine atmosphere investigated using the NO–NO₂–O₃ photostationary state

Abstract. The photostationary state (PSS) equilibrium between NO and NO2 is reached within minutes in the atmosphere can be described by PSS parameter, φ. Deviations from expected values of φ have previously been used to infer missing oxidants diverse locations, highly polluted regions extremely clean conditions observed remote marine boundary layer (MBL), interpreted as understanding fundamental photochemistry. Here, contrary these previous observations, we observe good agreement PSS-derived ([NO2]PSS ext.), calculated measured NO, O3, jNO2 photochemical box model predictions peroxy radicals (RO2 HO2), ([NO2]Obs.) air containing low levels CO (<90 ppbV) VOCs (volatile organic compounds). However, small amounts aged pollution (CO > 100 ppbV), higher than inferred PSS, with [NO2]Obs. / [NO2]PSS ext. 1.12–1.68 (25th–75th percentile), implying underestimation RO2 18.5–104 pptV. Potential measurement artefacts carefully considered when comparing NO2, but show that artefact required explain deviation would ∼ 4 times greater maximum known interferences. If additional convert a reaction rate equivalent methyl (CH3O2), then net ozone production (NOPR, ppbV h−1) including similar average change O3 observed, estimated uncertainties, once halogen oxide chemistry accounted for. This implies such cannot excluded oxidant modelled concentrations are significantly underestimated under conditions.