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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 1 | Copyright
Atmos. Meas. Tech., 11, 141-159, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 10 Jan 2018

Research article | 10 Jan 2018

Comparison of VOC measurements made by PTR-MS, adsorbent tubes–GC-FID-MS and DNPH derivatization–HPLC during the Sydney Particle Study, 2012: a contribution to the assessment of uncertainty in routine atmospheric VOC measurements

Erin Dunne, Ian E. Galbally, Min Cheng, Paul Selleck, Suzie B. Molloy, and Sarah J. Lawson Erin Dunne et al.
  • CSIRO Oceans and Atmosphere, Aspendale, 3195, Australia

Abstract. Understanding uncertainty is essential for utilizing atmospheric volatile organic compound (VOC) measurements in robust ways to develop atmospheric science. This study describes an inter-comparison of the VOC data, and the derived uncertainty estimates, measured with three independent techniques (PTR-MS, proton-transfer-reaction mass spectrometry; GC-FID-MS, gas chromatography with flame-ionization and mass spectrometric detection; and DNPH–HPLC, 2,4-dinitrophenylhydrazine derivatization followed by analysis by high-performance liquid chromatography) during routine monitoring as part of the Sydney Particle Study (SPS) campaign in 2012. Benzene, toluene, C8 aromatics, isoprene, formaldehyde and acetaldehyde were selected for the comparison, based on objective selection criteria from the available data. Bottom-up uncertainty analyses were undertaken for each compound and each measurement system. Top-down uncertainties were quantified via the inter-comparisons. In all seven comparisons, the correlations between independent measurement techniques were high with R2 values with a median of 0.92 (range 0.75–0.98) and small root mean square of the deviations (RMSD) of the observations from the regression line with a median of 0.11 (range 0.04–0.23ppbv). These results give a high degree of confidence that for each comparison the response of the two independent techniques is dominated by the same constituents. The slope and intercept as determined by reduced major axis (RMA) regression gives a different story. The slopes varied considerably with a median of 1.25 and a range of 1.16–2.01. The intercepts varied with a median of 0.04 and a range of −0.03 to 0.31ppbv. An ideal comparison would give a slope of 1.00 and an intercept of 0.

Some sources of uncertainty that are poorly quantified by the bottom-up uncertainty analysis method were identified, including: contributions of non-target compounds to the measurement of the target compound for benzene, toluene and isoprene by PTR-MS as well as the under-reporting of formaldehyde, acetaldehyde and acetone by the DNPH technique. As well as these, this study has identified a specific interference of liquid water with acetone measurements by the DNPH technique.

These relationships reported for Sydney 2012 were incorporated into a larger analysis with 61 similar published inter-comparison studies for the same compounds. Overall, for the light aromatics, isoprene and the C1–C3 carbonyls, the uncertainty in a set of measurements varies by a factor of between 1.5 and 2. These uncertainties ( ∼ 50%) are significantly higher than uncertainties estimated using standard propagation of error methods, which in this case were  ∼ 22% or less, and are the result of the presence of poorly understood or neglected processes that affect the measurement and its uncertainty. The uncertainties in VOC measurements identified here should be considered when assessing the reliability of VOC measurements from routine monitoring with individual, stand-alone instruments; when utilizing VOC data to constrain and inform air quality and climate models; when using VOC observations for human exposure studies; and for comparison with satellite retrievals.

Publications Copernicus
Short summary
A comparison of measurements of 7 volatile organic compounds (VOCs) in urban air by 3 different methods is presented. An uncertainty was calculated for each method and VOCs measured to provide some idea of the reliability of the data. Even when this uncertainty was accounted for, the measurements from the different methods did not agree for 4 of the 7 VOCs. Thus, there is unaccounted uncertainty in VOC measurements which must be considered when utilizing the data and assessing their reliability.
A comparison of measurements of 7 volatile organic compounds (VOCs) in urban air by 3 different...