Abstract

Abstract. The α-dicarbonyl compounds glyoxal (CHOCHO) and methyl glyoxal (CH3C(O)CHO) are produced in the atmosphere by the oxidation of hydrocarbons and emitted directly from pyrogenic sources. Measurements of ambient concentrations inform about the rate of hydrocarbon oxidation, oxidative capacity, and secondary organic aerosol (SOA) formation. We present results from a comprehensive instrument comparison effort at two simulation chamber facilities in the US and Europe that included nine instruments, and seven different measurement techniques: broadband cavity enhanced absorption spectroscopy (BBCEAS), cavity-enhanced differential optical absorption spectroscopy (CE-DOAS), white-cell DOAS, Fourier transform infrared spectroscopy (FTIR, two separate instruments), laser-induced phosphorescence (LIP), solid-phase micro extraction (SPME), and proton transfer reaction mass spectrometry (PTR-ToF-MS, two separate instruments; for methyl glyoxal only because no significant response was observed for glyoxal). Experiments at the National Center for Atmospheric Research (NCAR) compare three independent sources of calibration as a function of temperature (293–330 K). Calibrations from absorption cross-section spectra at UV-visible and IR wavelengths are found to agree within 2% for glyoxal, and 4% for methyl glyoxal at all temperatures; further calibrations based on ion–molecule rate constant calculations agreed within 5% 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 or methyl glyoxal, R2 > 0.96), and in complex gas mixtures characteristic of dry photochemical smog systems (o-xylene/NOx and isoprene/NOx, R2 > 0.95; R2 ∼ 0.65 for offline SPME measurements of methyl glyoxal). The correlations are more variable in humid ambient air mixtures (RH > 45%) for methyl glyoxal (0.58 < R2 < 0.68) than for glyoxal (0.79 < R2 < 0.99). The intercepts of correlations were insignificant for the most part (below the instruments' experimentally determined detection limits); slopes further varied by less than 5% for instruments that could also simultaneously measure NO2. For glyoxal and methyl glyoxal the slopes varied by less than 12 and 17% (both 3-σ) between direct absorption techniques (i.e., calibration from knowledge of the absorption cross section). We find a larger variability among in situ techniques that employ external calibration sources (75–90%, 3-σ), and/or techniques that employ offline analysis. Our intercomparison reveals existing differences in reports about precision and detection limits in the literature, and enables comparison on a common basis by observing a common air mass. Finally, we evaluate the influence of interfering species (e.g., NO2, O3 and H2O) of relevance in field and laboratory applications. Techniques now exist to conduct fast and accurate measurements of glyoxal at ambient concentrations, and methyl glyoxal under simulated conditions. However, techniques to measure methyl glyoxal at ambient concentrations remain a challenge, and would be desirable.

Highlights

  • The α-dicarbonyl compounds, glyoxal (CHOCHO, GLY) and methyl glyoxal (CH3C(O)CHO, MGLY), are produced in the atmosphere by the oxidation of hydrocarbons from biogenic, anthropogenic and pyrogenic sources (Volkamer et al, 2007; Fu et al, 2008; Myriokefalitakis et al, 2008; Stavrakou et al, 2009; Washenfelder et al, 2011)

  • The data from all instruments was analyzed by the individual groups and correlations were calculated with respect to cavity-enhanced differential optical absorption spectroscopy (CE-DOAS) for the data from National Center for Atmospheric Research (NCAR) and between each instrument pair for the European Photoreactor (EUPHORE) experiments

  • The CE-DOAS, PTR-ToF-MS and Fourier Transform Infrared Spectrometer (FTIR) instruments at NCAR used independent sources of calibration, and provide an opportunity to assess our understanding of the underlying absorption cross-section data at UV-visible and IR wavelengths, as well as compare these cross sections with ion– molecule rate constants

Read more

Summary

Introduction

The α-dicarbonyl compounds, glyoxal (CHOCHO, GLY) and methyl glyoxal (CH3C(O)CHO, MGLY), are produced in the atmosphere by the oxidation of hydrocarbons from biogenic (isoprene), anthropogenic (toluene, xylenes, acetylene) and pyrogenic sources (Volkamer et al, 2007; Fu et al, 2008; Myriokefalitakis et al, 2008; Stavrakou et al, 2009; Washenfelder et al, 2011). Glyoxal and methyl glyoxal measurements have been conducted for almost 30 years (Tuazon and Atkinson, 1990a; Yu et al, 1997), but sensitive and robust in situ techniques suitable to measure these compounds with high time resolution as part of field observations have only become available over the past decade (Volkamer et al, 2005a; Washenfelder et al, 2008; Huisman et al, 2008; Thalman and Volkamer, 2010; Baidar et al, 2013; Henry et al, 2012; DiGangi et al, 2012; Ahlm et al, 2012). This work addresses these issues of common language for limits of detection, assesses some likely measurement interferences, calibration standards and general instrument performance in a series of simulation chamber experiments carried out at the National Center for Atmospheric Research (NCAR) reaction chamber in Boulder, Colorado, USA and the Instituto Universitario Universitas Miguel Hernandez-Centro de Estudios Ambientales del Mediterraneo (UMH-CEAM) European Photoreactor (EUPHORE) in Valencia, Spain

Methods
Results
Discussion
Conclusion
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call