Final Report: Emission and Fate of Biogenic Volatile Organic Compounds

EPA Grant Number: R825419
Title: Emission and Fate of Biogenic Volatile Organic Compounds
Investigators: Lamb, Brian , Westberg, Hal
Institution: Washington State University
EPA Project Officer: Shapiro, Paul
Project Period: November 1, 1996 through October 31, 1999
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


The overall objective of this project was to improve our ability to predict biogenic hydrocarbon emissions throughout the United States. Specific objectives included: (1) field verification of biogenic emissions inventory system (BEIS) emission models at various U.S. locations; (2) investigation of seasonal isoprene emission patterns; and (3) further evaluation and development of hydrocarbon flux measurement techniques.

Summary/Accomplishments (Outputs/Outcomes):

A major emphasis in this work involved participation in the National Science Foundation (NSF) Program for Research on Oxidants, known as Photochemistry, Emissions, and Transport (PROPHET). As part of the PROPHET program, three measurement techniques were used to determine isoprene fluxes over a northern deciduous forest: (1) direct comparison of two tower based methods; (2) relaxed eddy accumulation (REA) and eddy covariance (EC); and (3) yielded standard isoprene flux estimates that varied by less than 15 percent. This is excellent consistency for two different flux techniques. In addition, diurnal emission patterns obtained by the two methods concurred. Standard emission fluxes of 12.2 (REA 1998), 10.6 (EC 1998), and 7.3 (REA 1997) mgm-2">-2hr-1 were determined at the PROPHET site. The 7.3 value represents a very limited number of measurements and is, therefore, less reliable than the higher values. Based on the 1998 measurements, we would recommend using a standard flux value of 11.4 mgm-2hr-1 for this northern hardwood forest regime. With an aspen and oak isoprene emitting a biomass density of approximately 150 gm-2, a standard emission rate of 76 mgg-1hr-1 should be used for estimating regional isoprene emissions.

Our isoprene emission flux of 11.4 mgm-2hr-1 is comparable with the standard emission flux of 12.4 mgm-2hr-1 (10.9 mgCm-2hr-1 ) reported for the Harvard Forest site (Goldstein, et al., 1998). Isoprene emitting biomass in the Harvard Forest is predominantly oak, which may cause some enhancement in emissions when compared to the aspen dominated canopy at the PROPHET site. These standard fluxes are larger than the value of 5.3 mgCm-2hr-1 (a total VOC emission of 7.0 with isoprene contribution of 75 percent) suggested for northern mixed forest ecosystems by Guenther, et al. (1994). However, a very recent report, Isebrands, et al. (1999) determined a standard isoprene emission rate of 87 µgg-1hr-1 (77.5 mgCg-1hr-1) from aspen leaves at a mixed deciduous forest site in northern Wisconsin. This is slightly higher than the average value of 76 µgg-1hr-1 that we obtained by combining our 1998 REA and EC results at the PROPHET site. Thus, the recent studies at PROPHET, Harvard Forest, and Wisconsin indicate that a standard isoprene flux of about 12 mgm-2hr-1 (10.5 mgCm-2hr-1) is appropriate for northern forests containing substantial quantities of aspen and/or oak.

Six aircraft flights provided isoprene profile measurements over the PROPHET site. This data was used with a mixed layer gradient model to estimate isoprene fluxes at the landscape scale. While limited in scope, the monotonic Lagrangian grid (MLG) results yielded values similar to REA isoprene fluxes measured during the same time frame. The range of MLG determined fluxes (0.9-1.8 mgm-2hr-1) is similar to the mean value 1.9 mgCm-2hr-1 obtained using the same modeling approach at a mixed hardwood forest site in northern Wisconsin (Isebrands, et al., 1999).

The use of eddy covariance has provided more detailed insight into emission variability during the daytime period. It was fairly common to have large changes (factor of two) in the measured isoprene flux from one half-hour period to the next. In most cases, this fluctuating pattern was not correlated with sunlight or temperature.

As a result of this work, and with additional support from NSF, a database of isoprene, carbon dioxide, water vapor, and sensible heat fluxes was developed. The database covers approximately 6 weeks during 1998, and the entire growing seasons during 1999, 2000, and 2001 at the University of Michigan Biological Station PROPHET site. Future research efforts will focus on exploiting this database to find explanations for the variability in isoprene emission patterns.

In addition to the flux measurements made at PROPHET, extensive flux measurements were made from the canopy of a managed Poplar stand in rural northeastern Oregon during the 1995 to 1999 seasons. Fluxes were measured primarily with the REA method. During some periods, comparison measurements were made using the flux gradient technique and with an EC method using a fast isoprene sensor. Concentrations of isoprene were measured using gas chromatograph-flame ionization detector as the primary analytical technique.

High fluxes of isoprene were recorded with values reaching 35 mgCm-2 hr-1. Concentrations reached 140 ppbv during the hottest days when winds were low. Emission and concentrations varied substantially on a diurnal basis with highest levels of each corresponding to mid-afternoon periods with higher temperatures and solar radiation. Isoprene concentrations and fluxes often decreased abruptly in the early evening.

Biomass additions during subsequent growing seasons appear to result in a corresponding change in the standardized isoprene flux. The standard flux for 30°C and photosynthetically active radiation (PAR) equal to 1000 µmolm-2s-1">-1changed from approximately 4 mgCm-2hr-1 in 1995 to 10.5 mgCm-2hr-1 in 1998. The relationship of the standard flux to cumulative historical ambient temperatures was investigated. The most favorable correlation was exhibited for a 7 day running mean temperature and the measured isoprene flux (r2 = 0.69). Isoprene as a portion of the net ecosystem exchange of carbon also was explored. For the 1996 growing season, the cumulative isoprene flux was approximately 1.6 percent of the cumulative carbon exchange.

Isoprene flux measurements, obtained through a U.S. Environmental Protection Agency cooperative agreement, received further analysis as part of this grant. Leaf, canopy, and mixed-layer scale isoprene emission measurements were collected over 3 weeks in the summer during an experimental scale-up emission study at the Walker Branch Forest near Oak Ridge, TN, in 1995. At the canopy scale, concurrent isoprene flux measurements were obtained with two independent REA systems and with a modified Bowen ratio gradient method. Fluxes measured with the two REA systems showed consistency, but were larger than those measured with the gradient method, possibly because of differences in the effective measurement height.

The REA results were used with detailed biomass density data to evaluate the performance of three canopy models: the Biogenic Emissions Inventory System (BEIS2), using ambient temperature and light attenuated through the canopy; the Canadian Biogenic Emissions Inventory System (CANBEIS), using leaf temperature and light attenuated through the canopy; and CANOAK, based upon an explicit numerical treatment of forest canopy dynamics. The CANBEIS and CANOAK models showed somewhat better performance than BEIS2, for isoprene-emitting biomass treated as a function of up wind direction sector. Overall, the CANBEIS model results were within 30 percent of the mean observed flux, within 15 percent of the maximum observed flux, and within 2 percent of the mean of the top 10 flux measurements. Use of a back trajectory footprint model to assign biomass density for each measurement period did not significantly improve these results. Measured leaf temperatures were as much as 1.5°C warmer than local air temperature in the upper canopy during midday, and as much as 1.5°C cooler than local air temperature in the evening. Modeled temperatures for a shaded leaf using CANOAK showed correspondence with the observations; however, for a sunlit leaf, the predicted leaf temperatures were much higher than the average observations.

Journal Articles on this Report : 4 Displayed | Download in RIS Format

Other project views: All 24 publications 5 publications in selected types All 5 journal articles
Type Citation Project Document Sources
Journal Article Apel EC, Riemer DD, Hills A, Baugh W, Orlando J, Faloona I, Tan D, Brune W, Lamb B, Westberg H, Carroll MA, Thornberry T, Cooper O, Geron CD. Measurement and interpretation of isoprene fluxes and isoprene, methacrolein and methyl vinyl ketone mixing ratios at the PROPHET site during the 1998 intensive. Journal of Geophysical Research 2002;107(D3):Art.No.4034. R825419 (Final)
R825261 (Final)
  • Abstract: American Geophysical Union Abstract
  • Journal Article Barket Jr. DJ, Hurst JM, Couch TL, Colorado A, Shepson PB, Riemer DD, Hills AJ, Apel EC, Hafer R, Lamb BK, Westberg HH, Farmer CT, Stabenau ER, Zika RG. Intercomparison of automated methodologies for determination of ambient isoprene during the PROPHET 1998 summer campaign. Journal of Geophysical Research–Atmospheres 2001;106(D20):24301-24313. R825419 (Final)
    R825256 (1999)
    R825256 (Final)
    R825257 (Final)
  • Full-text: Wiley-Full Text PDF
  • Abstract: Wiley-Abstract
  • Journal Article Hurst JM, Barket Jr. DJ, Herrera-Gomez O, Couch TL, Shepson PB, Faloona I, Tan D, Brune W, Westberg H, Lamb B, Biesenthal T, Young V, Goldstein A, Munger JW, Thornberry T, Carroll MA. Investigation of the nighttime decay of isoprene. Journal of Geophysical Research–Atmospheres 2001;106(D20):24335-24346. R825419 (Final)
    R825256 (1999)
    R825256 (Final)
  • Full-text: Wiley-Full Text PDF
  • Abstract: Wiley-Abstract
  • Other: Harvard University-Full Text PDF
  • Journal Article Westberg H, Lamb B, Hafer R, Hills A, Shepson P, Vogel C. Measurement of isoprene fluxes at the PROPHET site. Journal of Geophysical Research 2001;106(D20):24347-24358. R825419 (Final)
  • Abstract:
  • Supplemental Keywords:

    atmosphere, ozone, isoprene, volatile organic compounds, VOC, biogenic VOC emissions, relaxed eddy accumulation, eddy covariance, midwest, hardwood forest, aspen, oak, fluxes., RFA, Scientific Discipline, Air, Ecosystem Protection/Environmental Exposure & Risk, Environmental Chemistry, Ecosystem/Assessment/Indicators, Ecosystem Protection, Ecological Effects - Environmental Exposure & Risk, Ecological Effects - Human Health, tropospheric ozone, Biology, Engineering, Ecological Indicators, fate, fate and transport, Biogenic Emission Inventory System, biogenic modeling, ambient air, measurement of oxygenated compounds, ozone, VOCs, air sampling, oxidants, emissions model, ballon sampling, emissions inventory, multi-scale emission measurement, oxidant, vegetation

    Relevant Websites: Exit

    Progress and Final Reports:

    Original Abstract
  • 1997 Progress Report
  • 1998 Progress Report