This project is a collaborative effort involving investigators from four institutions with complimentary expertise in measuring and interpreting biogenic volatile organic carbon (BVOC) compounds and associated reaction products. The project is envisioned as part of a longer-term research initiative designed to test the following hypothesis: "The impact of BVOC emissions on climate depends on the structures of the BVOC; while isoprene can impact ozone production, terpenes are more effective at nitrogen sequestration and aerosol production; the change to terpene-dominance in forests will lead to more carbon sequestration, other factors remaining the same." During year 1, the principal investigators (PIs) will construct and test in the laboratory an automated measurement system consisting of a sampling apparatus, a two-dimensional gas chromatograph (GCxGC), and a calibration system to quantify ambient mixing ratios of speciated BVOCs and reaction products hourly. The sampling apparatus will concentrate BVOCs and reaction products and transfer to a GC fitted with two secondary columns. One channel will feed a flame ionization detector (FID) to quantify BVOCs and the other an electron capture detector (ECD) to quantify oxidation products (including nitrates and hydroxynitrate). The general utility calibration source will include a temperature-controlled bath containing multiple compound-specific diffusion tubes and associated plumbing. During year 2, the PIs will deploy and continuously operate this novel semi-autonomous measurement system at the Program for Research on Oxidants: PHotochemistry, Emissions, & Transport (PROPHET) site at the University of Michigan Biological Station (UMBS) over a 4-week period during the growing season. The goal of the field deployment will be to test the instrument's performance in reliably quantifying a broad suite of heavy alkanes, alkenes, aromatics, isoprene, montoterpenes, sesquiterpenes, aldehydes and ketones, and alcohols, and organic nitrates in ambient air within and above the forest canopy.
The development of a semi-autonomous measurement system for BVOCs and reaction products will enhance observational resolution for investigations of interactions among forest dynamics, oxidation processes, aerosol production, nitrogen and carbon sequestration, and associated feedbacks on climate. Results from the project will also extend the PROPHET data archive, which has been a valuable community resource for broader investigations of forest-atmosphere interactions. Graduate and undergraduate students will participate directly in constructing and field testing the instrument. Results will be disseminated through articles in the scientific literature and also incorporated into an inquiry-based instructional webquest to help high school students understand biosphere-atmosphere research in the context of global climate change. This webquest would become part of a library of similar educational resources at UMBS.
", was to design and build a device that can do long-term, low-maintenance measurements of substances in the atmosphere that affect air quality. Air quality is a product of the interactions of many species found in air; some natural in origin and some man-made. In our studies, we are interested in the natural, or biogenic, substances. Biogenic compounds are emitted into the atmosphere primarity by vegetation. While there is much vegetation in the biosphere, the amount of biogenic compounds emitted is relatively small. This situation makes measuring them a difficult, yet important challenge. While their emission concentrations are small, these emitted substances are generally very reactive and have a large impact on air quality. In particular, our goal is to see how biogenic emissions change over the long term; especially during a transition from one type of vegetation to another. Northern Michigan used to be forested by oak and white pine as the dominate species of trees. Logging cleared these species out and other, faster growing trees took their place. Aspen overtook the forest because of its ability to sprout from roots and runners. Aspen also happens to be a strong emitter of isoprene, a very reactive biogenic compound. Aspen is also relatively short-lived and is currently dying out. In its place, oak and white pine are returning to the forest understory, and will eventually replace the aspen as the dominate tree species. As this conversion takes place, the emissions and, thus, the chemistry of the atmosphere will change. It is the change that we wish to monitor. This desire leads us back to the original goal of designing and building an instrument that can do long-term studies. This change in the forest is not instantaneous. To capture the change and judge its effects on air quality requires that we have a robust means of capturing and quantifying the biogenic emissions. It also meant that we needed a way to separate out the very complex mixture of trace compounds that one finds in the atmosphere. To this end, we built an instrument for the collection, concentrating, and measuring of biogenic compounds (Figure 1) and deployed it at the University of Michigan Biological Station in Pellston, MI (UMBS, Figure 2) and at the Southern Oxidants and Aerosol Study (SOAS) site in Brent, AL (Figure 3). The initial work at UMBS was a "shake-down" of the instrument and our methods. The SOAS study was the first opportunity to truly utilize the abilities of the instrument. In all, we partially achieved our goals. We built a new instrument that can repetitively capture and quantitate gas-phase species over time. We have deployed it for long stretches of time. It is not a maintenance free as we would like, however. For our future work, we would like to continue reengineering the instrument to make it more robust. We would also like funding to permit our original goal of long-term monitoring at the UMBS site.
