Measurements of a potential interference with laser-induced fluorescence measurements of ambient OH from the ozonolysis of biogenic alkenes

Reactions of the hydroxyl radical (OH) play a central role in the chemistry of the atmosphere, and mea- surements of its concentration can provide a rigorous test of our understanding of atmospheric oxidation. Several re- cent studies have shown large discrepancies between mea- sured and modeled OH concentrations in forested areas im- pacted by emissions of biogenic volatile organic compounds (BVOCs), where modeled concentrations were significantly lower than measurements. A potential reason for some of these discrepancies involves interferences associated with the measurement of OH using the laser-induced fluorescence– fluorescence assay by gas expansion (LIF-FAGE) technique in these environments. In this study, a turbulent flow reac- tor operating at atmospheric pressure was coupled to a LIF- FAGE cell and the OH signal produced from the ozonoly- sis of $\alpha$-pinene, $\beta$-pinene, ocimene, isoprene, and 2-methyl- 3-buten-2-ol (MBO) was measured. To distinguish between OH produced from the ozonolysis reactions and any OH arti- fact produced inside the LIF-FAGE cell, an external chem- ical scrubbing technique was used, allowing for the di- rect measurement of any interference. An interference un- der high ozone (between 2 × 10$^{13}$ and 10 × 10$^{13}$ cm$^{−3}$) and BVOC concentrations (between approximately 0.1 × 10$^{12}$ and 40 × 10$^{12}$ cm$^{−3}$) was observed that was not laser gen- erated and was independent of the ozonolysis reaction time. For the ozonolysis of $\alpha$ and $\beta$-pinene, the observed inter- ference accounted for approximately 40 % of the total OH signal, while for the ozonolysis of ocimene the observed in- terference accounted for approximately 70 % of the total OH signal. Addition of acetic acid to the reactor eliminated the interference, suggesting that the source of the interference in these experiments involved the decomposition of stabilized Criegee intermediates (SCIs) inside the FAGE detection cell. Extrapolation of these measurements to ambient concentra- tions suggests that these interferences should be below the detection limit of the instrument.

Publication Date:
Jan 03 2018
Date Submitted:
Mar 03 2019
Atmospheric Measurement Techniques, 11, 1

 Record created 2019-03-03, last modified 2019-04-03

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