A new technique for the selective measurement of atmospheric peroxy radical concentrations of HO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and RO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; using a denuding method

K Miyazaki,A E Parker,C Fittschen,P S Monks,Y Kajii

doi:10.5194/amt-3-1547-2010

Abstract

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.

Highlights

Peroxy radicals RO2 play an important role in the photo-oxidation cycles of the troposphere (Monks, 2005)
An improvement to the well-established Peroxy radical chemical amplification (PERCA) technique allowing the selective measurement of HO2 and RO2 radical concentrations has been described in this paper
Three different materials have been tested to investigate the variation of the removal efficiency as a function of relative humidity

Summary

Introduction

NO via reaction with peroxy radicals is an important source of tropospheric ozone, a major constituent of photochemical oxidants that are detrimental to human health and contribute to global warming. Peroxy radical chemical amplification (PERCA) originated by Cantrell and Stedman (1982) is a method of measuring the total concentration of peroxy radicals, i.e. the sum of HO2 and RO2. Recent studies of PERCA have reported a greater wall loss rate of HO2 relative to RO2. The greater wall loss rate of HO2 relative to RO2 can be actively used to separate HO2 and RO2 during atmospheric measurements by predominantly denuding HO2 prior to the PERCA inlet. This makes it possible to measure the concentration of RO2 separately from the sum of HO2 and RO2, and obtain the ambient concentrations of HO2 and RO2. The practical utility of the developed instrument is evaluated through atmospheric measurements of HO2 and RO2 radicals

Experimental

Results and discussion

Ambient measurement

Conclusions