Instrument intercomparison of glyoxal, methyl glyoxal and NO2 under simulated atmospheric conditions

[摘要] The α-dicarbonyl compounds glyoxal (CHOCHO) and methyl glyoxal(CH₃C(O)CHO) are produced in the atmosphere by the oxidation ofhydrocarbons and emitted directly from pyrogenic sources. Measurements ofambient concentrations inform about the rate of hydrocarbon oxidation,oxidative capacity, and secondary organic aerosol (SOA) formation. Wepresent results from a comprehensive instrument comparison effort at twosimulation chamber facilities in the US and Europe that included nineinstruments, and seven different measurement techniques: broadband cavityenhanced absorption spectroscopy (BBCEAS), cavity-enhanced differentialoptical absorption spectroscopy (CE-DOAS), white-cell DOAS, Fouriertransform infrared spectroscopy (FTIR, two separate instruments), laser-induced phosphorescence (LIP), solid-phase micro extraction (SPME), andproton transfer reaction mass spectrometry (PTR-ToF-MS, two separateinstruments; for methyl glyoxal only because no significant response wasobserved for glyoxal). Experiments at the National Center for AtmosphericResearch (NCAR) compare three independent sources of calibration as a functionof temperature (293–330 K). Calibrations from absorption cross-sectionspectra at UV-visible and IR wavelengths are found to agree within 2% forglyoxal, and 4% for methyl glyoxal at all temperatures; furthercalibrations based on ion–molecule rate constant calculations agreed within5% for methyl glyoxal at all temperatures. At the European Photoreactor(EUPHORE) all measurements are calibrated from the same UV-visible spectra(either directly or indirectly), thus minimizing potential systematic bias.We find excellent linearity under idealized conditions (pure glyoxal ormethyl glyoxal, R² > 0.96), and in complex gas mixturescharacteristic of dry photochemical smog systems (o-xylene/NO_x andisoprene/NO_x, R² > 0.95; R² ∼ 0.65for offline SPME measurements of methyl glyoxal). The correlations are morevariable in humid ambient air mixtures (RH > 45%) for methylglyoxal (0.58 < R² < 0.68) than for glyoxal (0.79 < R² < 0.99). The intercepts of correlations wereinsignificant for the most part (below the instruments' experimentallydetermined detection limits); slopes further varied by less than 5% forinstruments that could also simultaneously measure NO₂. For glyoxal andmethyl glyoxal the slopes varied by less than 12 and 17% (both3-σ) between direct absorption techniques (i.e., calibration fromknowledge of the absorption cross section). We find a larger variabilityamong in situ techniques that employ external calibration sources (75–90%,3-σ), and/or techniques that employ offline analysis. Ourintercomparison reveals existing differences in reports about precision anddetection limits in the literature, and enables comparison on a common basisby observing a common air mass. Finally, we evaluate the influence ofinterfering species (e.g., NO₂, O₃ and H₂O) of relevance infield and laboratory applications. Techniques now exist to conduct fast andaccurate measurements of glyoxal at ambient concentrations, and methylglyoxal under simulated conditions. However, techniques to measure methylglyoxal at ambient concentrations remain a challenge, and would bedesirable.

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