OH- radical reactivity with total volatile org. compds. (VOC), SkVOC[VOC], is directly obtained in the planetary boundary layer (PBL). A method is based on a perturbation technique where high initial OH- concns. are created by flash photolysis of O3 and subsequent reaction of O(1D) with H2O. Laser-induced fluorescence measures residual OH- concn. at different time delays after the perturbation (<100 ms) to obtain a direct est. of OH- lifetime (tOH) under different atm. conditions. For specific exptl. conditions, transport by wind may be neglected, and chem. processes governing OH- decay may be expressed using a detailed box model. With a simple chem. equation derived using tOH and complementary measurements of CO, O3, and NOx, an in-situ est. of SkVOC[VOC] in the PBL is retrieved with an uncertainty <20% vs. detailed box model calcns. This anal. was applied to lab. measurements with 3 synthetic NOx/VOC/O3 gas mixts.; retrieved OH- lifetimes and total VOC reactivity are discussed against model predictions.