 |
NARSTO Workshop on Innovative Methods for Emission Inventory Development and Evaluation University of Texas, Austin October 14-17, 2003 |
 |
Direct Flux Measurements of Volatile Organic Compounds
B. Lamb, S. Pressley, E. Velasco, E. Allwine, and H. Westberg
Washington State University
T. Jobson, M. Alexander, and P. Prazellor
Pacific Northwest National Laboratory
Eddy covariance (EC) flux methods and fast response chemical sensors have matured to the point where it is now possible to make direct emission measurements of a range of volatile organic compounds (VOCs). In addition, new variations on EC methods, called disjunct eddy covariance (DEC), provide further flexibility in coupling a variety of chemical sampling methods or sensors to turbulence measurements to yield direct emission measurements. These EC and DEC methods provide a way to obtain direct measurement of VOC fluxes from forested environments and the potential to yield similar data for urban environments. Because these systems can be operated in a continuous, automated manner, long term measurements covering a wide range of conditions are possible. The source footprints from EC/DEC methods generally extend from a few hundred meters to several kilometers and, as such, the data provide a basis for direct evaluation of emission models and/or gridded emission inventories. In this presentation, EC flux measurements of isoprene and associated CO2, H2O, and heat fluxes from a northern deciduous forest are presented that cover complete growing seasons from 1999 through 2003. To illustrate the potential of these methods in urban environments, preliminary results from an urban flux tower operated for several weeks in Mexico City will also be discussed. In the Mexico City study, a fast alkene sensor was employed in EC mode and a proton transfer reaction mass spectrometer (PTR-MS) was used in DEC mode to measure various VOC fluxes in a densely populated section of Mexico City.