Chamber Studies of NO3 reactivity during the oxidation of isoprene

Isoprene is the major volatile organic compound that is released into the environment via biogenicemissions and its oxidation can result in formation of secondary organic aerosol (SOA). Althoughisoprene emission occurs mainly at daytime, it can accumulate at nighttime and be oxidized by thenitrate radical (NO3) to form organic nitrates that can partition to the particle phase. A detailedunderstanding of the reaction between isoprene and NO3 is thus required to predict its role in e.g.NOX lifetimes and SOA formation.The reaction between NO3 and isoprene was investigated under varying experimental conditions(high or low RO2/HO2, temperature, humidity, seed aerosols) during the NO3ISOP campaign at theatmospheric simulation chamber SAPHIR of the research centre in Julich (Germany). Directmeasurement of the NO3 reactivity was carried out with means of a flowtube coupled to a cavity-ring-down spectroscopy (FT-CRDS) setup which enabled the evolution of the NO3 lifetime duringthe isoprene oxidation process to be monitored.By comparing direct NO3 reactivity measurements with those calculated from VOC mixing ratiosand those calculated from a stationary-state analysis we identify the contributions of isoprene,secondary oxidation products and peroxy radicals to NO3 losses