Articles | Volume 10, issue 10
Atmos. Meas. Tech., 10, 3985–4000, 2017
Atmos. Meas. Tech., 10, 3985–4000, 2017

Research article 27 Oct 2017

Research article | 27 Oct 2017

A new method for atmospheric detection of the CH3O2 radical

Lavinia Onel1, Alexander Brennan1, Paul W. Seakins1,2, Lisa Whalley1,2, and Dwayne E. Heard1,2 Lavinia Onel et al.
  • 1School of Chemistry, University of Leeds, Leeds, LS2 9JT, UK
  • 2National Centre for Atmospheric Science, University of Leeds, LS2 9JT, UK

Abstract. A new method for measurement of the methyl peroxy (CH3O2) radical has been developed using the conversion of CH3O2 into CH3O by excess NO with subsequent detection of CH3O by fluorescence assay by gas expansion (FAGE) with laser excitation at ca. 298 nm. The method can also directly detect CH3O, when no nitric oxide is added. Laboratory calibrations were performed to characterise the FAGE instrument sensitivity using the conventional radical source employed in OH calibration with conversion of a known concentration of OH into CH3O2 via reaction with CH4 in the presence of O2. Detection limits of 3.8 × 108 and 3.0 × 108 molecule cm−3 were determined for CH3O2 and CH3O respectively for a signal-to-noise ratio of 2 and 5 min averaging time. Averaging over 1 h reduces the detection limit for CH3O2 to 1.1 × 108 molecule cm−3, which is comparable to atmospheric concentrations. The kinetics of the second-order decay of CH3O2 via its self-reaction were observed in HIRAC (Highly Instrumented Reactor for Atmospheric Chemistry) at 295 K and 1 bar and used as an alternative method of calibration to obtain a calibration constant with overlapping error limits at the 1σ level with the result of the conventional method of calibration. The overall uncertainties of the two methods of calibrations are similar – 15 % for the kinetic method and 17 % for the conventional method – and are discussed in detail. The capability to quantitatively measure CH3O in chamber experiments is demonstrated via observation in HIRAC of CH3O formed as a product of the CH3O2 self-reaction.

Short summary
Methyl peroxy (CH3O2) radicals are the most abundant organic peroxy radical species and are critical intermediates in rapid chemical cycling at the heart of tropospheric oxidation. Despite their importance, at present CH3O2 radicals are not specifically measured in the atmosphere by any direct or indirect method. This work presents a new method for the selective and sensitive detection of CH3O2 radicals and its use for the measurement of CH3O2 in the atmospheric simulation chamber HIRAC.