A new method for atmospheric detection of the CH<sub>3</sub>O<sub>2</sub> radical

Abstract

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 / O2. Detection limits of 3.8 × 108 molecule cm−3 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 hour reduces the detection limit for CH3O2 to 1.1 × 108 molecule cm−3 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.

Detection of RO2 radicals and other products from cyclohexene ozonolysis with NH4+ and acetate chemical ionization mass spectrometry

“…Very recently new methods for measurement of peroxy radicals (RO 2 ) focusing on less oxidized RO 2 were presented. Onel et al (2017) (H 2 O) n with n = 1-5 as adduct ions to softly ionize RO 2 radicals. The detection sensitivity of each RO 2 radical was estimated by titration with NO and varied from 0.05 to 1 cps/pptv, with an uncertainty of a factor of 3-5.…”