Investigation of a potential HCHO measurement artifact from ISOPOOH.

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

doi:10.5194/amt-9-4561-2016

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 (RH= 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 2013 September 6 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 for <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 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.

Highlights

Formaldehyde (HCHO) in the atmosphere is predominantly a product of the gas-phase oxidation of volatile organic compounds (VOCs)
Accurate in situ HCHO measurements in isoprene-rich environments are crucial for refining our understanding of biogenic emissions and chemistry (Kaiser et al, 2015; Wolfe et al, 2016)
The experimental results for ISOPOOH conversion to HCHO and the laboratory time constant are discussed in the context of data from the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4 RS) campaign (Toon et al, 2016)

Summary

Introduction

Formaldehyde (HCHO) in the atmosphere is predominantly a product of the gas-phase oxidation of volatile organic compounds (VOCs). Oxidation of methane produces a global background of HCHO that accounts for ∼ 80 % of the global. The emissions of non-methane hydrocarbons (NMHCs), such as isoprene and its oxidation products, are more localized and create spatial heterogeneity in HCHO production due to their shorter atmospheric lifetime. HCHO is one of the few VOCs that can be measured from orbit (e.g., Chance et al., 2000), and is used to estimate global isoprene emissions from space (Marais et al, 2012; Millet et al, 2008; Palmer et al., 2003, 2006). Accurate in situ HCHO measurements in isoprene-rich environments are crucial for refining our understanding of biogenic emissions and chemistry (Kaiser et al, 2015; Wolfe et al, 2016)

Methods

Results

Conclusion