Total VOC reactivity in the planetary boundary layer 1. Estimation by a pump and probe OH experiment

Abstract

The reactivity of hydroxyl radical (OH) with total volatile organic compounds (VOC), ΣkVOC[VOC], is directly obtained in the planetary boundary layer (PBL). The method is based on a perturbation technique where high initial OH concentrations are created by flash photolysis of ozone and subsequent reaction of O(1D) with H2O. Laser-induced fluorescence is used to measure the residual OH concentration at different time delays after the perturbation (<100 ms) and obtain a direct estimate of the OH lifetime τOH for different atmospheric conditions. For specific experimental conditions the transport by the wind may be neglected, and the chemical processes governing the OH decay may be expressed by a detailed box model. With a simple chemical equation derived in this paper using τOH and complementary measurements of CO, O3, and NOx, an in situ estimate of ΣkVOC[VOC] in the PBL is retrieved with an uncertainty of less than 20% in comparison to the detailed box model calculations. This analysis is applied to laboratory measurements with three synthetic NOx/VOC/O3 gas mixtures, and the retrieved OH lifetimes and total VOC reactivity are discussed against model predictions. Copyright 2001 by the American Geophysical Union.