Inferring the diurnal variability of OH radical concentrations over the Amazon from BVOC measurements

Abstract The atmospheric oxidation of biogenic volatile organic compounds (BVOC) by OH radicals over tropical rainforests impacts local particle production and the lifetime of globally distributed harmful and radiatively active gases. For the pristine Amazon rainforest during the dry season, we empirically determined the diurnal OH radical variability at the forest-atmosphere interface region between 80 and 325m from 07:00 to 15:00 LT using BVOC measurements. A dynamic time warping approach was applied showing that median averaged transport times between 80 m to 325 m decrease from 105 to 15 minutes over this time period. The inferred OH concentrations show evidence for an early morning OH peak (07:00–08:00 LT) and an OH maximum (13:00–14:00LT) reaching 1x106 ± 1.1x106 molecules cm− 3 controlled by the coupling between BVOC emission fluxes, convective turbulence, air chemistry and photolysis rates. The results were evaluated against a turbulence resolving transport (DALES), a regional scale (WRF-Chem) and a global (EMAC) atmospheric chemistry model.