A new technique for the selective measurement of atmospheric peroxy radical concentrations of HO₂ and RO₂ using a denuding method

Abstract. A technique for the selective measurement of atmospheric HO₂ and RO₂ using peroxy radical chemical amplification coupled to laser-induced fluorescence NO₂ detection (PERCA-LIF) is demonstrated. By pulling the air through a filled pre-inlet advantage can be taken of the higher heterogeneous loss rate of HO₂ relative to CH₃O₂. Pre-inlet conditions have been found where ca. 90% of HO₂ was removed whereas the comparable CH₃O₂ loss was 15%. The dependence of loss rate on humidity and peroxy radical concentration has been investigated. When using glass beads as the surface for peroxy radical removal, the influence of the relative humidity on the removal efficiency becomes negligible. It may therefore be possible to apply this technique to the measurement of absolute concentrations of solely RO₂ as well as the sum of HO₂ and RO₂. The practical utility of the PERCA-LIF coupled to a denuder has been demonstrated with atmospheric measurements.