1997 Progress Report: Emission and Fate of Biogenic Volatile Organic CompoundsEPA Grant Number: R825419
Title: Emission and Fate of Biogenic Volatile Organic Compounds
Investigators: Lamb, Brian , Claiborn, Candis , Westberg, Hal
Current Investigators: Lamb, Brian , Westberg, Hal
Institution: Washington State University
EPA Project Officer: Shapiro, Paul
Project Period: November 1, 1996 through October 31, 1999
Project Period Covered by this Report: November 1, 1996 through October 31, 1997
Project Amount: $372,986
RFA: Exploratory Research - Air Engineering (1996) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Land and Waste Management , Air , Engineering and Environmental Chemistry
Objective:The purpose of this work is to improve our understanding of the emissions of biogenic volatile organic compounds (BVOC) from vegetation and, in turn, to evaluate and improve the Biogenic Emission Inventory System (BEIS) as it is applied in various US locations.
Work during the past year has occurred in three areas: 1) participation in the PROPHET field program, 2) assistance with the NARSTO assessment of biogenic hydrocarbon emissions, and 3) incorporation of results from related research programs conducted at WSU. In the first area, WSU participated in the PROPHET 1997 summer intensive in north-central Michigan. PROPHET (Program for Research on Oxidants: PHotochemistry, Emissions and Transport) is a multi-investigator research effort with NARSTO affiliation that is aimed at understanding the formation and transport of photochemical air pollutants in the central US (http://aoss.engin.umich.edu/PROPHET/). The PROPHET field site is at the University of Michigan biological research station which is located in the midst of a mixed deciduous forest. During the summer field intensive, WSU conducted isoprene and terpene canopy-scale flux measurements using a relaxed eddy accumulation (REA) system, measured ambient VOC concentrations above the canopy on a diurnal basis, collected a series of branch enclosure emission samples to fingerprint VOC emissions from each of the dominant tree species, and conducted a biomass inventory in the vicinity of the PROPHET tower site. Results from this work will be presented at the spring AGU meeting in Boston during May, 1998.
In the second area, WSU assisted with writing the draft NARSTO assessment document (Guenther et al., 1997) for biogenic emissions of ozone precursors. The purpose of this assessment is to describe current understanding and identify critical areas needed for improvement in the development of biogenic emission inventory systems. The assessment document was presented at the NARSTO assessment meeting in Miami in November, 1997. The document will be submitted for publication in Atmospheric Environment as part of a NARSTO special issue. As part of this assessment process, a new version of the inventory, BEIS3 is under development. WSU is involved in this development.
In the third area, results from three other WSU research programs are being used in our overall effort to improve BEIS and as part of our contribution to the NARSTO assessment activities. First, seasonal isoprene emission rates were obtained during the summer and fall at a hybrid poplar plantation near Boardman, OR. Fluxes were measured using the WSU REA system and, in the fall, direct eddy correlation with a fast isoprene analyzer. These data are being used to test BEIS emission canopy models. In addition, cooperative measurements with NCAR were conducted of leaf level emissions using leaf cuvette systems. Downwind plume measurements of isoprene and oxidation products were also collected with NCAR during one day to investigate the overall impact of the poplar plantation upon the local air quality. Results from a recent cooperative field program with NCAR, EPA, and NOAA investigators at a mixed deciduous forest near Oak Ridge, TN were also summarized and presented at the International Workshop on Biogenic Hydrocarbons held in Charlottesville, VA during August, 1997 (Lamb et al., 1997). These activities were supported through an EPA cooperative agreement.
Second, terpene emissions data were collected using a branch cuvette system at an old growth Douglas fir forest in the Cascades of Washington state in conjunction with the Western Regional Global Climate Change Program sponsored by DOE. The goal of the program is to obtain a complete description of carbon cycling in this ecosystem. The unique feature of this work was access to the full height of the 60 m canopy using the Wind River Canopy Research Facility. Diurnal sampling was conducted on Douglas fir and western hemlock trees throughout the summer and fall, 1997. Visits to the site occurred at approximately 3.5 week intervals. Results from this work are being used to expand the BEIS data base for assigning standard emission factors for terpenes from these tree species and to determine the distribution of terpenes emitted from these species.
Third, new tree inventory data for western Washington were used to revise BEIS2 for application in a regional photochemical air quality model. Results from ambient sampling of detailed individual hydrocarbons collected at a variety of surface stations throughout western Washington during 1996 and 1997 were used to evaluate the overall accuracy of BEIS2. Data from a two week intensive tethered balloon sampling study were also used in this evaluation. The results from this analysis were presented at the BVOC workshop described above.
Accomplishments and Research Results: Preliminary analyses of isoprene fluxes measured during the PROPHET field program show that fluxes predicted with BEIS2 show relatively good agreement with the observations when the biomass distribution in the vicinity of the tower is incorporated. At the same, the diurnal pattern of isoprene emissions shows some significant departures from the pattern predicted with BEIS2. Terpene flux measurements suggest that emissions from the local forest were negligible and that deposition of terpenes advected from upwind dominated the observed fluxes. These may provide the basis for the first estimate of terpene deposition rates to a forest canopy.
The evaluation of BEIS2 in western Washington, after revision with new tree inventory distributions, show relatively consistent agreement between the emission inventory and ambient observations. These evaluations were based upon 1) comparisons of the ratio of isoprene/a-pinene in ambient air and in the inventory, 2) comparison of isoprene fluxes estimated from mixed layer modeling of balloon sampling data with those in the emission inventory, 3) comparison of the BVOC ambient concentrations with those predicted using the regional photochemical grid model (in terms of a lumped VOC representing the sum of isoprene and terpenes). This work is valuable for demonstrating a combination of methods for evaluating BEIS and for showing the importance of updating BEIS vegetation class distributions in the western US.
Terpene emissions from Douglas fir and hemlock were in relatively good agreement with the values used in the current BEIS2 for these vegetation types. The distribution of terpenes emitted from Douglas fir were dominated (in order) by -pinene, 3-carene, -pinene, and limonene, while those from hemlock were dominated (in order ) by -pinene, limonene, -pinene, and myrcene.