Peroxy Radical Measurements during the IRRONIC Field Project by C2H6 - NO Chemical Amplification

Abstract:

We present measurements of total peroxy radicals (HO₂ + RO₂) during the Indiana Radical, Reactivity and Ozone Production Intercomparison (IRRONIC) field project in Bloomington, Indiana during July 2015. Peroxy radicals were measured by chemical amplification using ethane and nitric oxide in dual PFA reaction chambers, and the amplification product NO₂ was quantified by cavity attenuated phase shift spectroscopy. On sunny days mid-day peroxy radical mixing ratios were typically between 20 and 70 ppt and were well correlated with “HO₂*” measured by the Indiana University Laser-Induced Fluorescence with Fluorescence Assay by Gas Expansion (IU-FAGE) instrument. The ratio of total peroxy radicals (UMass) to the IU-FAGE HO₂* measurements was greater than two. We also describe results from an informal intercomparison of the two instruments’ calibration sources, which are based on acetone photolysis (UMass) and water photolysis (IU). In addition to sampling the IU calibration source in “amplification” mode, the UMass instrument also separately quantified the HO₂ mixing ratio in the IU calibration gas by reaction with excess NO and subsequent quantification of the NO₂ produced.