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<p>OH reactivity (OHR) is an important control on the oxidative capacity in the atmosphere but remains poorly constrained in many environments, such as remote, rural, and urban atmospheres, as well as laboratory experiment setups under low-NO conditions. For an improved understanding of OHR, its evolution during oxidation of volatile organic compounds (VOCs) is a major aspect requiring better quantification. We use the fully explicit Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A) model to study the OHR evolution in the NO-free photooxidation of several VOCs, including decane (an alkane), <span class="inline-formula"><i>m</i></span>-xylene (an aromatic), and isoprene (an alkene). Oxidation progressively produces more saturated and functionalized species. Total organic OHR (including precursor and products, <span class="inline-formula">OHR_VOC</span>) first increases for decane (as functionalization increases OH rate coefficients) and <span class="inline-formula"><i>m</i></span>-xylene (as much more reactive oxygenated alkenes are formed). For isoprene, <span class="inline-formula">C=C</span> bond consumption leads to a rapid drop in <span class="inline-formula">OHR_VOC</span> before significant production of the first main saturated multifunctional product, i.e., isoprene epoxydiol. The saturated multifunctional species in the oxidation of different precursors have similar average <span class="inline-formula">OHR_VOC</span> per C atom. The latter oxidation follows a similar course for different precursors, involving fragmentation of multifunctional species to eventual oxidation of C1 and C2 fragments to <span class="inline-formula">CO₂</span>, leading to a similar evolution of <span class="inline-formula">OHR_VOC</span> per C atom. An upper limit of the total OH consumption during complete oxidation to <span class="inline-formula">CO₂</span> is roughly three per C atom. We also explore the trends in radical recycling ratios. We show that differences in the evolution of <span class="inline-formula">OHR_VOC</span> between the atmosphere and an environmental chamber, and between the atmosphere and an oxidation flow reactor (OFR), can be substantial, with the former being even larger, but these differences are often smaller than between precursors. The Teflon wall losses of oxygenated VOCs in chambers result in large deviations of <span class="inline-formula">OHR_VOC</span> from atmospheric conditions, especially for the oxidation of larger precursors, where multifunctional species may suffer substantial wall losses, resulting in significant underestimation of <span class="inline-formula">OHR_VOC</span>. For OFR, the deviations of <span class="inline-formula">OHR_VOC</span> evolution from the atmospheric case are mainly due to significant OHR contribution from <span class="inline-formula">RO₂</span> and lack of efficient organic photolysis. The former can be avoided by lowering the UV lamp setting in OFR, while the latter is shown to be very difficult to avoid. However, the former may significantly offset the slowdown in fragmentation of multifunctional species due to lack of efficient organic photolysis.</p>