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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, D07301, doi:10.1029/2004JD005523, 2005

Long-term isoprene flux measurements above a northern hardwood forest

Shelley Pressley

Department of Civil and Environmental Engineering, Washington State University, Pullman, Washington, USA

Brian Lamb

Department of Civil and Environmental Engineering, Washington State University, Pullman, Washington, USA

Hal Westberg

Department of Civil and Environmental Engineering, Washington State University, Pullman, Washington, USA

Julia Flaherty

Department of Civil and Environmental Engineering, Washington State University, Pullman, Washington, USA

Jack Chen

Department of Civil and Environmental Engineering, Washington State University, Pullman, Washington, USA

Christoph Vogel

University of Michigan Biological Station, University of Michigan, Pellston, Michigan, USA

Abstract

We report continuous whole canopy isoprene emission fluxes from a northern hardwood forest in Michigan for the 1999–2002 growing seasons. The eddy covariance fluxes of isoprene, CO₂, latent heat, and sensible heat are presented along with an analysis of the seasonal and year-to-year variations. Measurements were made in collaboration with the AmeriFlux site located at the University of Michigan Biological Station (UMBS) and the Program for Research on Oxidants: PHotochemistry, Emissions, and Transport (PROPHET). In general, isoprene emissions increased throughout the day with increasing temperature and light levels, peaked at midafternoon, and declined to zero by night. There were significant variations from one 30-min period to the next, and from one day to the next. Average midday isoprene fluxes were 2.8, 3.2, and 2.9 mg C m⁻² h⁻¹ for 2000 through 2002, respectively. Insufficient data were available to include 1999. Last frost and full leaf out were significantly later in 2002 compared to the other years; however, total accumulated isoprene emissions for each year varied by less than 10%. Fully developed isoprene emissions occurred between 400 and 500 heating degree days, roughly half those required at other sites. Using long-term net ecosystem exchange measurements from the UMBS∼Flux group, isoprene emissions represent between 1.7 to 3.1% of the net carbon uptake at this site. Observations for 2000–2002 were compared with the BEIS3 emission model. Estimates agree well with observations during the midsummer period, but BEIS3 overestimates observations during the spring onset of emissions and the fall decline in emissions. This work provides a unique long-term data set useful for verifying canopy scale models and to help us better understand the dynamics of biosphere-atmosphere exchange of isoprene.

Received 12 October 2004; accepted 13 January 2005; published 2 April 2005.

Keywords: eddy covariance; isoprene; biogenic hydrocarbons.

Index Terms: 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions (0426, 1610); 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 3322 Atmospheric Processes: Land/atmosphere interactions (1218, 1631, 1843); 3379 Atmospheric Processes: Turbulence (4490); 3394 Atmospheric Processes: Instruments and techniques.

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Citation: Pressley, S., B. Lamb, H. Westberg, J. Flaherty, J. Chen, and C. Vogel (2005), Long-term isoprene flux measurements above a northern hardwood forest, J. Geophys. Res., 110, D07301, doi:10.1029/2004JD005523.

Copyright 2005 by the American Geophysical Union.