A new method for atmospheric detection of the CH3O2 radical

作者:Onel Lavinia*; Brennan Alexander; Seakins Paul W; Whalley Lisa; Heard Dwayne E*
来源:Atmospheric Measurement Techniques, 2017, 10(10): 3985-4000.
DOI:10.5194/amt-10-3985-2017

摘要

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 O-2. Detection limits of 3.8 x 10(8) and 3.0 x 10(8) 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 x 10(8) 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 295K and 1 bar and used as an alternative method of calibration to obtain a calibration constant with overlapping error limits at the 1 sigma 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.

  • 出版日期2017-10-27