Measurements of Peroxy Radicals Using Chemical Amplification−Cavity Ringdown Spectroscopy

Abstract

The peroxy radical chemical amplification (PERCA) method is combined with cavity ringdown spectroscopy(CRDS) to detect peroxy radicals (HO2 and RO2). In PERCA, HO2 and RO2 are first converted to NO2 via reactions with NO, and the OH and RO coproducts are recycled back to HO2 in subsequent reactions with CO and O2; the chain reactions of HO2 are repeated and amplify the level of NO2. The amplified NO2 is then monitored by CRDS, a sensitive absorption technique. The PERCA-CRDS method is calibrated using a HO2 radical source (0.5-3 ppbv), which is generated by thermal decomposition of H2O2 vapor (permeated from 2% H2O2 solution through a porous Teflon tubing) up to 600 degrees C. Using a 2-m long 6.35-mm o.d. Teflon tubing as the flow reactor and 2.5 ppmv NO and 2.5-10% vol/vol CO, the PERCA amplification factor or chain length, Delta[NO2]/([HO2]+[RO2]), is determined to be 150 +/- 50 (90% confidence limit) in this study. The peroxy radical detection sensitivity by PERCA-CRDS is estimated to be approximately 10 pptv/60 s (3sigma). Ambient measurements of the peroxy radicals are carried out at Riverside, California in 2007 to demonstrate the PERCA-CRDS technique.

A new technique for the selective measurement of atmospheric peroxy radical concentrations of HO<sub>2</sub> and RO<sub>2</sub> using a denuding method

“…The NO 2 product is then quantified by the appropriate measurement technique, e.g. luminol chemiluminescence (Parker et al, 2009), laser-induced fluorescence (Sadanaga et al, 2004) and cavity-ring-down (Liu et al, 2009) spectroscopy. In order to obtain absolute concentrations, the chain length of the amplification and the response of the NO 2 detector has to be determined in calibration experiments.…”

Peroxy radical detection for airborne atmospheric measurements using absorption spectroscopy of NO<sub>2</sub>

“…The PeRCEAS instrument reported by Liu et al (2009) differs both in scope (airborne measurements for PeRCEAS vs. ground-based measurements) and general layout (pressure stabilized inlet of PeRCEAS vs. Teflon tubing inlet, compact 19 NO 2 detector with a diode laser for PeRCEAS vs. more voluminous Nd-YAG pumped dye laser setup). Its chain length is reported to be 150 ± 50 for standard pressure.…”

“…A similar configuration using the PeRCA technique and a CRDS NO 2 detector (albeit without optical feedback) is described in Liu et al (2009), who reported on an instrument for ground-based measurements at standard pressure. It is a combination of a NO 2 CRDS detector (Hargrove et al, 2006) and a 5 m-long (Teflon) tubing system enabling the peroxy radical chemical conversion.…”

Global analysis of peroxy radicals and peroxy radical-water complexation using the STOCHEM-CRI global chemistry and transport model

“…A knowledge of peroxy radical abundances and distributions is essential to determine the oxidising capacity of the lower atmosphere in general (Thompson, 1992) and to determine oxidation rates and hence transformations of primary pollutants on a variety of scales. In spite of their importance in the chemical processing of the troposphere, there are few measurement data available (Cantrell et al, 1992(Cantrell et al, , 1996Carpenter et al, 1997;Zanis et al, 1999;Burkert et al, 2001Burkert et al, , 2003Hanke et al, 2002;Handisides et al, 2003;Mihelcic et al, 2003;Green et al, 2003;Fleming et al, 2006aFleming et al, , 2006bKukui et al, 2008;Liu et al, 2009;Andres-Hernandez et al, 2001. The reported abundances of peroxy radicals during different field studies have large variability and apart from Electron Spin Resonance (ESR) type studies (e.g.…”