Field measurements of methylglyoxal using Proton Transfer Reaction-Time of Flight Mass Spectrometry and comparison to the DNPH/HPLC-UV method

  • Michoud V
  • Sauvage S
  • Léonardis T
  • et al.
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Abstract

<p><strong>Abstract.</strong> Methylglyoxal (MGLY) is an important atmospheric α-dicarbonyl species whose photolysis acts as a significant source of peroxy radicals, contributing to the oxidizing capacity of the atmosphere and, as such, the formation of secondary pollutants such as organic aerosols and ozone. However, despite its importance, only a few techniques exhibit time resolutions and detection limits that are suitable for atmospheric measurements. <br><br> This study present, to the best of our knowledge, the first measurements of ambient MGLY using Proton Transfer Reaction-Time of Flight Mass Spectrometry (PTR-ToFMS). These measurements were performed during the ChArMEx SOP2 field campaign. This campaign took place at a Mediterranean site characterized by intense biogenic emissions and low levels of anthropogenic trace gases. Concomitant measurements of MGLY were performed using the 2,4-dinitrophenylhydrazine (DNPH) derivatization technique and High Performance Liquide Chromatography (HPLC) with UV detection. PTR-ToFMS and DNPH-HPLC measurements were compared to determine whether these techniques can perform reliable measurements of MGLY. <br><br> Ambient time series revealed levels of MGLY ranging from 28&amp;ndash;365<span class="thinspace"></span>pptv, with a clear diurnal cycle due to elevated concentrations of primary biogenic species during daytime, whose oxidation led to large production rates of MGLY. A scatter plot of the PTR-ToFMS and DNPH-HPLC measurements indicates a reasonable correlation (R<sup>2</sup><span class="thinspace"></span>=<span class="thinspace"></span>0.48) but a slope significantly lower than unity (0.58<span class="thinspace"></span>±<span class="thinspace"></span>0.05) and a significant intercept of 88.3<span class="thinspace"></span>±<span class="thinspace"></span>8.0<span class="thinspace"></span>pptv. A careful investigation of the differences between the two techniques suggests that this disagreement is not due to spectrometric interferences from H<sub>3</sub>O<sup>+</sup>(H<sub>2</sub>O)<sub>3</sub>, MEK (or butanal) detected at m/z 73.050 and m/z 73.065, respectively, which are close to the MGLY m/z of 73.029. The differences are more likely due to uncorrected sampling artefacts such as overestimated collection efficiency or loss of MGLY into the sampling line for the DNPH-HPLC technique or unknown isobaric interfering compounds such as acrylic acid and propanediol for the PTR-ToFMS. <br><br> Calculations of MGLY loss rates with respect to OH-oxidation and direct photolysis indicate similar contributions for these two loss pathways.</p>

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Michoud, V., Sauvage, S., Léonardis, T., Fronval, I., Kukui, A., Locoge, N., & Dusanter, S. (2018). Field measurements of methylglyoxal using Proton Transfer Reaction-Time of Flight Mass Spectrometry and comparison to the DNPH/HPLC-UV method. Atmospheric Measurement Techniques Discussions, 1–26. https://doi.org/10.5194/amt-2017-442

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