The rate constant for the reaction of OH with 3‐methylfuran was measured at 2, 4, and 6 Torr using discharge‐flow techniques coupled with laser‐induced fluorescence detection of OH. The measured rate constant (k) at 298 ± 2 K was (9.1 ± 0.3) × 10−11 cm3 molecule−1 s−1, where the quoted uncertainty reflects twice the standard error of the measurements. This result is in good agreement with previously reported relative rate constant measurements at atmospheric pressure and room temperature. An Arrhenius expression of k = (3.2 ± 0.4) × 10−11 e(310 ± 40)/T cm3 molecule−1 s−1 was determined from measurements of the rate constant between 273 and 368 K. The negative temperature dependence agrees with previously reported theoretical calculations for the reaction of OH with 3‐methylfuran and previously reported measurements of the temperature dependences of the rate constants for the reaction of OH with similar heterocyclic organics such as furan and thiophene.

Abstract. One technique used to measure concentrations of the hydroperoxy radical (HO2) in the atmosphere involves chemically converting it to OH by addition of NO and subsequent detection of OH. However, some organic peroxy radicals (RO2) can also be rapidly converted to HO2 (and subsequently OH) in the presence of NO, interfering with measurements of ambient HO2 radical concentrations. This interference must be characterized for each instrument to determine to what extent various RO2 radicals interfere with measurements of HO2 and to assess the impact of this interference on past measurements. The efficiency of RO2 to HO2 conversion for the Indiana University Laser-Induced Fluorescence – Fluorescence Assay by Gas Expansion (IU-FAGE) instrument was measured for a variety of RO2 radicals. Known quantities of OH and HO2 radicals were produced from the photolysis of water vapor at 184.9 nm, and RO2 radicals were produced by the reaction of several volatile organic compounds with OH. The conversion efficiency of RO2 radicals to HO2 was measured when NO was added to the sampling cell for conditions employed during several previous field campaigns. For these conditions, approximately 80 % of alkene derived RO2 radicals and 20 % of alkane derived RO2 radicals were converted to HO2. Based on these measurements, interferences from various RO2 radicals contributed to approximately 35 % of the measured HO2 signal during the Mexico City Metropolitan Area (MCMA) 2006 campaign, where the measured VOCs consisted of a mixture of saturated and unsaturated species. However, this interference can contribute more significantly to the measured HO2 signal in forested environments dominated by unsaturated biogenic emissions such as isoprene.