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Discussion papers
https://doi.org/10.5194/acp-2019-115
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-115
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 12 Feb 2019

Research article | 12 Feb 2019

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Chemistry and Physics (ACP).

On the sources and sinks of atmospheric VOCs: An integrated analysis of recent aircraft campaigns over North America

Xin Chen1, Dylan B. Millet1, Hanwant B. Singh2, Armin Wisthaler3,4, Eric C. Apel5, Elliot L. Atlas6, Donald R. Blake7, Steven S. Brown8, John D. Crounse9, Joost A. de Gouw8,10, Frank Flocke5, Alan Fried11, Brian G. Heikes12, Rebecca S. Hornbrook5, Tomas Mikoviny4, Kyung-Eun Min13, Markus Müller3,*, J. Andrew Neuman8,10, Daniel W. O'Sullivan14, Jeff Peischl8,10, Gabriele G. Pfister5, Dirk Richter12, James M. Roberts8, Thomas B. Ryerson8, Stephen Shertz15, Victoria Treadaway12, Patrick R. Veres8, James Walega11, Carsten Warneke8,10, Rebecca A. Washenfelder8, Petter Weibring11, and Bin Yuan16 Xin Chen et al.
  • 1Department of Soil, Water, and Climate, University of Minnesota, Minneapolis-Saint Paul, MN 55108, USA
  • 2NASA Ames Research Center, Moffett Field, CA, USA
  • 3Institute for Ion Physics and Applied Physics, University of Innsbruck, 6020 Innsbruck, Austria
  • 4Department of Chemistry, University of Oslo, Norway
  • 5Atmospheric Chemistry Observations & Modeling Laboratory, National Center for Atmospheric Research, Boulder, CO, 80301, USA
  • 6Department of Atmospheric Sciences, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, USA
  • 7Department of Chemistry, University of California, Irvine, Irvine, CA, USA
  • 8Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, CO 80305, USA
  • 9Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
  • 10Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, USA
  • 11Institute of Arctic & Alpine Research, University of Colorado, Boulder, CO
  • 12Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882, USA
  • 13School of Earth Science and Environmental Engineering, Gwangju Institute of Science and Technology
  • 14United States Naval Academy, Chemistry Department, Annapolis, MD, 21401, USA
  • 15Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, Colorado, USA
  • 16Institute for Environmental and Climate Research, Jinan University, Guangzhou, China
  • *now at: Ionicon Analytik GmbH, Innsbruck, Austria

Abstract. We apply a high-resolution chemical transport model (GEOS-Chem CTM) with updated treatment of volatile organic compounds (VOCs) and a comprehensive suite of airborne datasets over North America to i) characterize the VOC budget, and ii) test the ability of current models to capture the distribution and reactivity of atmospheric VOCs, over this region. Biogenic emissions dominate the North American VOC budget in the model, accounting for 70 % and 95 % of annually emitted VOC-carbon and reactivity, respectively. Based on current inventories anthropogenic emissions have declined to the point where biogenic emissions are the dominant summertime source of VOC reactivity even in most major North American cities. Methane oxidation is a 2× larger source of non-methane VOCs (via production of formaldehyde and methyl hydroperoxide) over North America in the model than are anthropogenic emissions. However, anthropogenic VOCs account for over half the ambient VOC loading over the majority of the region owing to their longer aggregate lifetime. Fires can be a significant VOC source episodically but are small on average. In the planetary boundary layer (PBL), the model exhibits skill in capturing observed variability in total VOC-abundance (R2 = 0.36) and reactivity (R2 = 0.54). The same is not true in the free troposphere (FT), where skill is low and there is a persistent low model bias (~ 60 %), with most (27 of 34) model VOCs underestimated by more than a factor of 2. A comparison of PBL : FT concentration ratios over the southeastern US points to a misrepresentation of PBL ventilation as a contributor to these model FT biases. We also find that a relatively small number of VOCs (acetone, methanol, ethane, acetaldehyde, formaldehyde, isoprene + oxidation products, methyl hydroperoxide) drive a large fraction of total ambient VOC reactivity and associated model biases; research to improve understanding of their budgets is thus warranted. A source tracer analysis suggests a current overestimate of biogenic sources for hydroxyacetone, methyl ethyl ketone and glyoxal, an underestimate of biogenic formic acid sources, and an underestimate of peroxyacetic acid production across biogenic and anthropogenic precursors. Future work to improve model representations of vertical transport and to address the VOC biases discussed are needed to advance predictions of ozone and SOA formation.

Xin Chen et al.
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Short summary
Volatile organic compounds (VOCs) affect air quality and modify the lifetimes of other pollutants. We combine a high-resolution 3D atmospheric model with an ensemble of aircraft observations to perform an integrated analysis of the VOC budget over North America. We find that biogenic emissions provide the main source of VOC reactivity even in most major cities. Our findings point to key gaps in current models related to oxygenated VOCs and to the distribution of VOCs in the free troposphere.
Volatile organic compounds (VOCs) affect air quality and modify the lifetimes of other...
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