Characterization of a chemical amplifier for peroxy radical measurements in the atmosphere

Abstract

Peroxy radicals (HO2 and RO2) are key species in atmospheric chemistry. They are produced during the oxidation of volatile organic compounds (VOCs) and are involved in the formation of photochemical pollutants such as ozone (O3) and secondary organic aerosols (SOA). However, ambient measurements of these reactive species are still challenging and only a few techniques can achieve both a good selectivity and a detection limit that is low enough for ambient measurements. In this publication we present the characterization of a Chemical Amplifier (CA) using two different approaches for ambient measurements of peroxy radicals, including the PEroxy Radical Chemical Amplifier (PERCA) and the Ethane based CHemical AMPlification (ECHAMP). At 50% Relative Humidity (RH), the experimental Chain Length (CL) for PERCA was found to be higher by approximately a factor of 3.7 compared to ECHAMP. The RH-dependence of the CL was also found to be larger for PERCA by a factor of 1.12. Box modeling of the chemistry taking place in the instrument highlighted that the formation of HNO3 from the HO2+NO reaction has a strong impact on the CL for both approaches. In addition, experiments conducted to quantify the RO2–to-HO2 conversion efficiency for a large range of organic peroxy radicals confirmed that it mainly depends on the organic nitrate (RONO2) formation yield, while the alkyl nitrite (RONO) yield is not limiting the CL in most cases. Ambient measurements using the PERCA approach are shown to illustrate the performances of this new instrument.