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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 9 | Copyright
Atmos. Meas. Tech., 11, 4943-4961, 2018
https://doi.org/10.5194/amt-11-4943-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 31 Aug 2018

Research article | 31 Aug 2018

The first evaluation of formaldehyde column observations by improved Pandora spectrometers during the KORUS-AQ field study

Elena Spinei1,2, Andrew Whitehill3, Alan Fried4, Martin Tiefengraber5,6, Travis N. Knepp7,8, Scott Herndon9, Jay R. Herman1,10, Moritz Müller5,6, Nader Abuhassan1,10, Alexander Cede1,5, Dirk Richter4, James Walega4, James Crawford7, James Szykman3,7, Lukas Valin3, David J. Williams3, Russell Long3, Robert J. Swap1, Youngjae Lee11, Nabil Nowak2, and Brett Poche2 Elena Spinei et al.
  • 1NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  • 2Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
  • 3US EPA, Research Triangle Park, Durham, NC 27709, USA
  • 4Institute of Arctic and Alpine Research (INSTAAR) at the University of Colorado, Boulder, C0 80303, USA
  • 5LuftBlick, Kreith 39A, 6162 Mutters, Austria
  • 6Institue of Atmospheric and Cryospheric Sciences, University of Innsbruck, Innsbruck, Austria
  • 7NASA Langley Research Center, Hampton, VA 23681, USA
  • 8Science Systems and Applications, Inc., Hampton, VA 23681, USA
  • 9Aerodyne Research, Inc., Billerica, MA 01821, USA
  • 10University of Maryland Baltimore County, Baltimore, MD, USA
  • 11Korean National Institute of Environmental Research (NIER), Incheon, South Korea

Abstract. The Korea–United States Air Quality Study (KORUS-AQ) conducted during May–June 2016 offered the first opportunity to evaluate direct-sun observations of formaldehyde (HCHO) total column densities with improved Pandora spectrometer instruments. The measurements highlighted in this work were conducted both in the Seoul megacity area at the Olympic Park site (37.5232°N, 27.1260°E; 26ma.s.l.) and at a nearby rural site downwind of the city at the Mount Taehwa research forest site (37.3123°N, 127.3106°E; 160ma.s.l.). Evaluation of these measurements was made possible by concurrent ground-based in situ observations of HCHO at both sites as well as overflight by the NASA DC-8 research aircraft. The flights provided in situ measurements of HCHO to characterize its vertical distribution in the lower troposphere (0–5km).

Diurnal variation in HCHO total column densities followed the same pattern at both sites, with the minimum daily values typically observed between 6:00 and 7:00 local time, gradually increasing to a maximum between 13:00 and 17:00 before decreasing into the evening. Pandora vertical column densities were compared with those derived from the DC-8 HCHO in situ measured profiles augmented with in situ surface concentrations below the lowest altitude of the DC-8 in proximity to the ground sites. A comparison between 49 column densities measured by Pandora vs. aircraft-integrated in situ data showed that Pandora values were larger by 16% with a constant offset of 0.22DU (Dobson units; R2 = 0.68). Pandora HCHO columns were also compared with columns calculated from the surface in situ measurements over Olympic Park by assuming a well-mixed lower atmosphere up to a ceilometer-measured mixed-layer height (MLH) and various assumptions about the small residual HCHO amounts in the free troposphere up to the tropopause. The best comparison (slope  = 1.03±0.03; intercept  = 0.29±0.02DU; and R2 = 0.78±0.02) was achieved assuming equal mixing within ceilometer-measured MLH combined with an exponential profile shape. These results suggest that diurnal changes in HCHO surface concentrations can be reasonably estimated from the Pandora total column and information on the mixed-layer height. More work is needed to understand the bias in the intercept and the slope relative to columns derived from the in situ aircraft and surface measurements.

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Formaldehyde is toxic to humans and is formed in the atmosphere in the presence of air pollution, but the measurements are sparse. Pandonia Global Network instruments measure total formaldehyde column from the surface to the top of troposphere and will be widely available. This study compared formaldehyde Pandora columns with the surface and aircraft-integrated columns near Seoul, South Korea. Relatively good agreement was observed between the three datasets with some overestimation by Pandora.
Formaldehyde is toxic to humans and is formed in the atmosphere in the presence of air...
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