Conversion of hydroperoxides to carbonyls in field and laboratory instrumentation: Observational bias in diagnosing pristine versus anthropogenically controlled atmospheric chemistry

Abstract

Atmospheric volatile organic compound (VOC) oxidation mechanisms under pristine (rural/remote) and urban (anthropogenically-influenced) conditions follow distinct pathways due to large differences in nitrogen oxide (NO x ) concentrations. These two pathways lead to products that have different chemical and physical properties and reactivity. Under pristine conditions, isoprene hydroxy hydroperoxides (ISOPOOHs) are the dominant first-generation isoprene oxidation products. Utilizing authentic ISOPOOH standards, we demonstrate that two of the most commonly used methods of measuring VOC oxidation products (i.e., gas chromatography and proton transfer reaction mass spectrometry) observe these hydroperoxides as their equivalent high-NO isoprene oxidation products -methyl vinyl ketone (MVK) and methacrolein (MACR). This interference has led to an observational bias affecting our understanding of global atmospheric processes. Considering these artifacts will help close the gap on discrepancies regarding the identity and fate of reactive organic carbon, revise our understanding of surface-atmosphere exchange of reactive carbon and SOA formation, and improve our understanding of atmospheric oxidative capacity.

Isoprene photochemistry over the Amazon rainforest

“…An additional issue is that the utility of existing data sets of MVK and MACR concentrations to test and constrain models of isoprene chemistry is challenged by recent laboratory studies that have shown that both PTR-MS and GC techniques can have a contribution from ISOPOOH species in the nominal detection of MVK and MACR (11,13). For the usual operating conditions of PTR-MS and GC instrumentation, the two main ISOPOOH isomers [specifically, (1-OH, 2-OOH)-ISOPOOH, hereafter (1, 2)-ISOPOOH, and (4-OH, 3-OOH)-ISOPOOH, hereafter (4, 3)-ISOPOOH] decompose on the hot metal surfaces inside both types of instruments (13).…”

“…For the usual operating conditions of PTR-MS and GC instrumentation, the two main ISOPOOH isomers [specifically, (1-OH, 2-OOH)-ISOPOOH, hereafter (1, 2)-ISOPOOH, and (4-OH, 3-OOH)-ISOPOOH, hereafter (4, 3)-ISOPOOH] decompose on the hot metal surfaces inside both types of instruments (13). The (1, 2)-ISOPOOH and (4, 3)-ISOPOOH decompose to MVK and MACR, respectively.…”

Overview of the Focused Isoprene eXperiment at the California Institute of Technology (FIXCIT): mechanistic chamber studies on the oxidation of biogenic compounds

“…ISOPOOH, IEPOX, and ISOPN were detected as either MAC or MVK in the GC-FID, depending on the specific isomer. The interferences may not be localized to this particular GCFID, and a more detailed account is forthcoming (Rivera et al, 2014). Conversion efficiencies of OVOCs to the C 4 carbonyls in the Caltech GC-FID range in order of ISOPOOH > IEPOX > ISOPN, and can be almost quantitative for ISOPOOH because of the facile cleavage of the weak O-O bond.…”

Identification of Organic Hydroperoxides and Peroxy Acids Using Atmospheric Pressure Chemical Ionization – Tandem Mass Spectrometry (APCI-MS/MS): Application to Secondary Organic Aerosol

“…Cumene hydroperoxide (80%), tert-butyl hydroperoxide (35%), 2-butanone peroxide (35%), peracetic acid (32%), di-tertbutyl peroxide (98%), benzoyl peroxide (≥98%), di(dodecanoyl) peroxide (97%), 2-nonenal (97%), meso-erythritol (≥99%), cis-pinonic acid (98%), formaldehyde (37%), acetaldehyde (>99%), hexanal (98%), methyl glyoxal (40%), glyoxal (40%), hydrogen peroxide (H 2 O 2, 30%), α-pinene (≥99%) and ammonium acetate (≥99.99%) are all purchased from Sigma-Aldrich (Canada). Isoprene-4-hydrox-3-hydroperoxide (ISOPOOH) is synthesized according to literature (Rivera-Rios et al, 2014). 5…”