Articles | Volume 17, issue 21
Atmos. Chem. Phys., 17, 13417–13438, 2017
Atmos. Chem. Phys., 17, 13417–13438, 2017

Research article 10 Nov 2017

Research article | 10 Nov 2017

Ethene, propene, butene and isoprene emissions from a ponderosa pine forest measured by relaxed eddy accumulation

Robert C. Rhew1, Malte Julian Deventer1,*, Andrew A. Turnipseed2,*, Carsten Warneke3,4, John Ortega5, Steve Shen1, Luis Martinez6, Abigail Koss3,4, Brian M. Lerner3,4,a, Jessica B. Gilman3,4, James N. Smith5,b, Alex B. Guenther7, and Joost A. de Gouw3 Robert C. Rhew et al.
  • 1Department of Geography and Berkeley Atmospheric Sciences Center, University of California Berkeley, Berkeley, CA 94720-4740, USA
  • 22B Technologies, Boulder CO 80301, USA
  • 3Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado Boulder, Boulder CO 80309, USA
  • 4NOAA Earth System Research Laboratory, Boulder, CO 80305, USA
  • 5Atmospheric Chemistry Observations and Modeling (ACOM), National Center for Atmospheric Research, Boulder, CO 80301, USA
  • 6Ernest F. Hollings Undergraduate Scholarship program, NOAA, Boulder, CO 80305, USA
  • 7Department of Earth System Science, University of California Irvine, Irvine, CA 92697-3100, USA
  • anow at: Aerodyne Research Inc., Billerica, MA 01821-3976, USA
  • bnow at: Department of Chemistry, University of California Irvine, Irvine, CA 92697-2025, USA
  • *These authors contributed equally to this work.

Abstract. Alkenes are reactive hydrocarbons that influence local and regional atmospheric chemistry by playing important roles in the photochemical production of tropospheric ozone and in the formation of secondary organic aerosols. The simplest alkene, ethene (ethylene), is a major plant hormone and ripening agent for agricultural commodities. The group of light alkenes (C2-C4) originates from both biogenic and anthropogenic sources, but their biogenic sources are poorly characterized, with limited field-based flux observations. Here we report net ecosystem fluxes of light alkenes and isoprene from a semiarid ponderosa pine forest in the Rocky Mountains of Colorado, USA using the relaxed eddy accumulation (REA) technique during the summer of 2014. Ethene, propene, butene and isoprene emissions have strong diurnal cycles, with median daytime fluxes of 123, 95, 39 and 17 µg m−2 h−1, respectively. The fluxes were correlated with each other, followed general ecosystem trends of CO2 and water vapor, and showed similar sunlight and temperature response curves as other biogenic VOCs. The May through October flux, based on measurements and modeling, averaged 62, 52, 24 and 18 µg m−2 h−1 for ethene, propene, butene and isoprene, respectively. The light alkenes contribute significantly to the overall biogenic source of reactive hydrocarbons: roughly 18 % of the dominant biogenic VOC, 2-methyl-3-buten-2-ol. The measured ecosystem scale fluxes are 40–80 % larger than estimates used for global emissions models for this type of ecosystem.

Short summary
Alkenes emanate from both natural and anthropogenic sources and can contribute to atmospheric ozone production. This study measured light alkene (ethene, propene and butene) fluxes from a ponderosa pine forest using a novel relaxed eddy accumulation method, revealing much larger emissions than previously estimated and accounting for a significant fraction of OH reactivity. Emissions have a diurnal cycle related to sunlight and temperature, and the forest canopy appears to be the source.
Final-revised paper