Articles | Volume 9, issue 9
Research article
16 Sep 2016
Research article |  | 16 Sep 2016

Investigation of a potential HCHO measurement artifact from ISOPOOH

Jason M. St. Clair, Jean C. Rivera-Rios, John D. Crounse, Eric Praske, Michelle J. Kim, Glenn M. Wolfe, Frank N. Keutsch, Paul O. Wennberg, and Thomas F. Hanisco

Abstract. Recent laboratory experiments have shown that a first generation isoprene oxidation product, ISOPOOH, can decompose to methyl vinyl ketone (MVK) and methacrolein (MACR) on instrument surfaces, leading to overestimates of MVK and MACR concentrations. Formaldehyde (HCHO) was suggested as a decomposition co-product, raising concern that in situ HCHO measurements may also be affected by an ISOPOOH interference. The HCHO measurement artifact from ISOPOOH for the NASA In Situ Airborne Formaldehyde instrument (ISAF) was investigated for the two major ISOPOOH isomers, (1,2)-ISOPOOH and (4,3)-ISOPOOH, under dry and humid conditions. The dry conversion of ISOPOOH to HCHO was 3 ± 2 % and 6 ± 4 % for (1,2)-ISOPOOH and (4,3)-ISOPOOH, respectively. Under humid (relative humidity of 40–60 %) conditions, conversion to HCHO was 6 ± 4 % for (1,2)-ISOPOOH and 10 ± 5 % for (4,3)-ISOPOOH. The measurement artifact caused by conversion of ISOPOOH to HCHO in the ISAF instrument was estimated for data obtained on the 6 September 2013 flight of the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) campaign. Prompt ISOPOOH conversion to HCHO was the source of < 4 % of the observed HCHO, including in the high-isoprene boundary layer. Time-delayed conversion, where previous exposure to ISOPOOH affects measured HCHO later in the flight, was conservatively estimated to be < 10 % of observed HCHO, and is significant only when high ISOPOOH sampling periods immediately precede periods of low HCHO.

Short summary
Global isoprene emissions are the largest source of atmospheric non-methane hydrocarbons. Lab results show that ISOPOOH, a low-NOx isoprene oxidation product, can decompose on instrument surfaces to form high-NOx isoprene oxidation products, causing misinterpretation of oxidation conditions. This study investigated the potential formaldehyde artifact from ISOPOOH for the NASA ISAF instrument, and found that it does not significantly affect the accuracy of the ISAF field measurements.