ABSTRACT

This project addresses biogenic emissions of volatile organic compounds (VOC), which will be measured at the Blodgett Forest site in central California. Fast response Proton-Transfer-Reaction Mass Spectrometers (PTR-MS) will be used for real-time in-situ measurements of concentrations and fluxes of biogenic VOCs, especially terpenes. These play important roles in the chemistry of the atmosphere by contributing to the cycling of important atmospheric radicals and tropospheric ozone, and through secondary organic aerosol formation. With earlier NSF support, field measurements of vertical concentration profiles through the forest canopy revealed the presence of large amounts of previously unreported oxidation products, which were also observed in smog chamber studies. The results suggest that about half the ecosystem scale ozone flux measured at Blodgett Forest in summer is due to chemical reactions of ozone with terpenes within the forest canopy, and that the flux of terpenes leaving the forest canopy represents only a small fraction of the terpenoid compounds actually emitted, while the rest is chemically processed within the forest canopy.
In the next phase of this research, the following objectives will be pursued:
1. The smog chamber research will be expanded to include full photochemical oxidation experiments in collaboration with Prof. Seinfeld at Caltech in order to identify even more of the relevant oxidation products under more representative atmospheric conditions;
2. The vertical flux of terpene oxidation products out of the forest canopy will be measured using the eddy covariance method; 3. New field measurements will be performed to observe the full suite of terpene oxidation products with a time response fast enough to observe their chemical transformations in the forest canopy; 4. Attempts will be made to identify the terpene oxidation products that have so far only been detected by their mass to charge ratio in the PTR-MS.
The Broader Impacts of this activity will be in the research providing important new constraints for models predicting the formation and distribution of secondary organic aerosol, models that estimate the effects of VOC emissions on regional air quality and global climate, as well as models predicting the response of biogenic VOC emissions to climate variability and change. Multiple collaborative research efforts at Blodgett Forest will be made possible or enhanced through this award. A postdoctoral researcher will be trained through this research. Undergraduate students will also be involved. Research methodologies and results generated from this project will be integrated into classroom teaching by Prof. Goldstein.

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