Intercomparison of peroxy radical instruments at the HELIOS atmospheric simulation chamber

International audience; Peroxy radicals (HO 2 and RO 2 ) are key species in atmospheric chemistry, which together with the hydroxyl radical (OH), are involved in oxidation processes leading to the formation of secondary pollutants such as ozone and organic aerosols. Monitoring these short-lived species during intensive field campaigns and comparing the measured concentrations to box model simulations allow assessing the reliability of chemical mechanisms implemented in atmospheric models. However, ambient measurements of peroxy radicals are still considered challenging and only a few techniques have been used for field measurements. Three complementary instruments capable of ambient measurements of pe roxy radicals have been deployed together at the HELIOS atmospheric simulation chamber (Orléans, France) in October 2018. These instruments rely on the PEroxy Radical Chemical Amplification (PERCA), Laser Induced Fluorescence-Fluorescent Assay by Gas Expansion (LIF-FAGE), and Chemical Ionisation Mass Spectrometry (CIMS) techniques. Several chamber experiments have been conducted under dark and irradiated conditions, including oxidation experiments of dihydrogen, methane, pentene, isoprene, and α-pinene. In this presentation, the agreement between the different instruments will be discussed in the light of supporting measurements of volatile organic compounds and inorganic species (O3, NO, NO2), photolysis frequencies, as well as box modelling of the chamber chemistry.