Biogenic Volatile Organic Compounds (BVOC) Data

Background

The measurement and modeling of Biogenic Volatile Organic Compounds (BVOC) are essential for understanding regional and global atmospheric chemistry, carbon cycles, and climate. For more than 40 years, research has been conducted to measure emissions of carbon-containing compounds (BVOC) from vegetation. This web site will provide a database of BVOC emission measurements and modeling parameters that is being developed by members of the biosphere-atmosphere interactions research community.

The enclosure database summarizes information from literature reports and identifies the plant species studied, the BVOC examined, the enclosure and analytical techniques applied, and other parameters considered. We have documented approximately 1800 plant species from which BVOC emissions have been studied thus far.

The database will also contain flux and concentration measurements from field studies. (The amount of study data available at this site is expected to increase in the future, and researchers are encouraged to include their observations in this effort). The creation of a central location for assessing and archiving this information should improve the utility of these data. The compiled datasets presented here will provide improved means for model evaluation and development. Eventually, these data will be used to develop community-consistent measurement protocols, procedures for quality assurance and submittal, and emissions information for use in and development of emissions and chemical models.

Reference

Wiedinmyer, C., Guenther, A., Harley, P., Hewitt, C.N., Geron, C., Artaxo, P., Steinbrecher, R., Rasmussen. (2004) Global organic emissions from vegetation. Chapter in Emissions of Atmospheric Trace Compounds, Edited by Claire Granier, Paulo Artaxo, and Claire E. Reeves. Kluwer Academic Publishers, Dordrecht, The Netherlands, pp. 115 -170.

Enclosure Measurements (Download)

The earliest studies of BVOC emissions from vegetation, conducted from the 1920s through the 1960s, used various types of enclosure systems to isolate individual leaves, branches or entire plants, and estimated emission rates from the increase in concentration over time. These enclosure systems were first used to estimate the total BVOC emission and the relative contribution of different BVOC, called the "fingerprint", for many plant species. Later studies, using dynamic flow through enclosures, began to characterize the relationships between emissions and environmental conditions, such as temperature and light. Enclosure studies continue to be the primary source of emission factors and emission algorithms used in BVOC emission models. Current studies continue to refine and improve existing measurement techniques and extend them into new landscapes and new chemical species. With increased understanding of additional environmental controls over BVOC emissions, enclosure studies are being used to develop new algorithms that account for a more complete set of driving variables. A separate list of publications and references is provided.

The data in the enclosure database are extracted directly from the literature, or provided directly from researchers. These data have not been thoroughly reviewed, and it is asked of all investigators to check the information included for their own research results. If there corrections or additions are to be made, please contact vocadmin@acd.ucar.edu

Above canopy flux measurements (Download Coming Soon)

Above canopy flux measurements have been used to quantify whole canopy BVOC fluxes and to evaluate emissions and chemical models. The earliest attempts to quantify whole canopy BVOC fluxes from above canopy measurements used indirect methods such as surface layer gradients and tracer ratios (e.g., Arnts et al. 1978, 1982). These methods relied on assumptions that could be met in ideal situations but were often violated. Although these initial flux measurements were difficult and labor intensive, and associated with uncertainties of 35% or more, they were extremely important for validating the general magnitude of whole canopy fluxes and establishing that the results of enclosure methods could be extrapolated with reasonable accuracy. Above canopy flux measurement techniques have improved considerably in recent years, the most significant advancement being the capability for direct measurements of BVOC fluxes using eddy covariance (e.g., Guenther and Hills 1998; Karl et al. 2000). These systems not only provide more accurate flux estimates but also enable continuous measurements and the ability to look at a wider range of BVOCs (e.g., oxygenated compounds). The primary use of above canopy flux measurements has been to evaluate and validate emission modeling procedures. However, these systems are now being used as the primary means of establishing area average emission factors in regions with high species diversity, such as tropical rainforests (Rinne et al. 2002), where it is difficult to characterize the emission characteristics of all of the tree species present.

The compiled datasets described in this and the previous section will provide improved means for model evaluation and development. Comments and suggestions are encouraged as these community datasets continue to evolve.

Ambient concentration measurements (Download Coming Soon)

The presence of BVOC in the atmospheric boundary layer has been used to demonstrate that emissions of these compounds directly influence the chemical composition of the atmosphere. The observed ambient levels are often misleading, however, since many of these compounds are very reactive and are present at very low levels in the atmosphere, even though their emission rates are substantial. Ambient concentration measurements are best used as a method for evaluating the combined predictions of emissions, chemistry and transport in numerical models. These observations are also sometimes used as the primary means of setting emission rates. This has notably been the case for tropical forests (e.g., Zimmerman et al. 1988) where more direct emission measurements have been made only recently.

There have been over 50 studies of ambient BVOC concentration measurements described in peer reviewed journals and more than 10 summarized in reports. Databases containing concentration measurements from individual studies are available to the scientific community for model testing, but they are few in number and difficult for most investigators to locate. The creation of a central site for accessing and archiving this information should improve the utility of these data. Study datasets containing available concentration measurements from a variety of studies are now available online (URL: bvoc.acd.ucar.edu). The amount of data available at this site is expected to increase in the future and researchers are encouraged to include their observations in this effort.

Acknowledgedments

The BVOC project is is sponsored by IGAC (International Global Atmospheric Chemistry) and it is supported by the NSF (National Science Foundation), the U.S. EPA (Enviromental Protection Agency) with contributions from Biosphere-Atmosphere Interactions Research Group at Lancaster University.