Missing peroxy radical sources within a rural forest canopy

Abstract Organic peroxy (RO 2 ) and hydroperoxy (HO 2 ) radicals are key intermediates in thephotochemical processes that generate ozone, secondary organic aerosol and reac-tive nitrogen reservoirs throughout the troposphere. In regions with ample biogenic 5 hydrocarbons, the richness and complexity of peroxy radical chemistry presents a sig- nificant challenge to current-generation models, especially given the scarcity of mea-surements in such environments. We present peroxy radical observations acquiredwithin a Ponderosa pine forest during the summer 2010 Bio-hydro-atmosphere inter-actions of Energy, Aerosols, Carbon, H 2 O, Organics and Nitrogen – Rocky Mountain 10 Organic Carbon Study (BEACHON-ROCS). Total peroxy radical mixing ratios reach as high as 180pptv and are among the highest yet recorded. Using the comprehen-sive measurement suite to constrain a near-explicit 0-D box model, we investigate thesources, sinks and distribution of peroxy radicals below the forest canopy. The basechemical mechanism underestimates total peroxy radicals by as much as a factor of