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Volume 15, issue 3 | Copyright

Special issue: The Pan European Gas-Aerosols Climate Interaction Study...

Atmos. Chem. Phys., 15, 1289-1298, 2015
https://doi.org/10.5194/acp-15-1289-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 06 Feb 2015

Research article | 06 Feb 2015

Evidence for an unidentified non-photochemical ground-level source of formaldehyde in the Po Valley with potential implications for ozone production

J. Kaiser1, G. M. Wolfe1,*,**, B. Bohn2, S. Broch2, H. Fuchs2, L. N. Ganzeveld3, S. Gomm2, R. Häseler2, A. Hofzumahaus2, F. Holland2, J. Jäger2, X. Li2, I. Lohse2, K. Lu2,***, A. S. H. Prévôt4, F. Rohrer2, R. Wegener2, R. Wolf4, T. F. Mentel2, A. Kiendler-Scharr2, A. Wahner2, and F. N. Keutsch1 J. Kaiser et al.
  • 1Chemistry, University of Wisconsin-Madison, Madison, WI, USA
  • 2Institut für Energie- und Klimaforschung Troposphäre IEK-8, Forschungszentrum Jülich GmbH, Jülich, Germany
  • 3Earth System Science and Climate Change, Wageningen University and Research Center, Wageningen, Netherlands
  • 4Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland
  • *now at: Joint Center for Earth Systems Technology, University of Maryland Baltimore County, Baltimore, MD, USA
  • **now at: Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA
  • ***now at: College of Environmental Sciences & Engineering, Peking University, Beijing, China

Abstract. Ozone concentrations in the Po Valley of northern Italy often exceed international regulations. As both a source of radicals and an intermediate in the oxidation of most volatile organic compounds (VOCs), formaldehyde (HCHO) is a useful tracer for the oxidative processing of hydrocarbons that leads to ozone production. We investigate the sources of HCHO in the Po Valley using vertical profile measurements acquired from the airship Zeppelin NT over an agricultural region during the PEGASOS 2012 campaign. Using a 1-D model, the total VOC oxidation rate is examined and discussed in the context of formaldehyde and ozone production in the early morning. While model and measurement discrepancies in OH reactivity are small (on average 3.4 ± 13%), HCHO concentrations are underestimated by as much as 1.5 ppb (45%) in the convective mixed layer. A similar underestimate in HCHO was seen in the 2002–2003 FORMAT Po Valley measurements, though the additional source of HCHO was not identified. Oxidation of unmeasured VOC precursors cannot explain the missing HCHO source, as measured OH reactivity is explained by measured VOCs and their calculated oxidation products. We conclude that local direct emissions from agricultural land are the most likely source of missing HCHO. Model calculations demonstrate that radicals from degradation of this non-photochemical HCHO source increase model ozone production rates by as much as 0.6 ppb h−1 (12%) before noon.

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Using measurements acquired from a Zeppelin airship during the PEGASOS 2012 campaign, we show that VOC oxidation alone cannot account for the formaldehyde concentrations observed in the morning over rural Italy. Vertical profiles suggest a ground-level source of HCHO. Incorporating this additional HCHO source into a photochemical model increases calculated O3 production by as much as 12%.
Using measurements acquired from a Zeppelin airship during the PEGASOS 2012 campaign, we show...
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