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.
This project funded the development, design, fabrication, and field testing of a new automated instrument that enables semi-continuous measurements of the concentrations of biogenic volatile organic compounds (BVOCs) in the atmosphere. These compounds are important, as they impact the concentrations of two pollutants regulated by the U.S. Clean Air Act, i.e. ozone and particulate matter. BVOCs are emitted by vegetation, mostly coniferous and deciduous trees. When they are oxidized in the atmosphere by OH radicals and ozone, they produce products that can lead to production of secondary organic aerosol, a type of particulate matter. And, this same oxidation process can, in the presence of nitric oxide (mostly derived from combustion of fossil fuels), produce ozone. Thus, to study the impact of forests and their emissions on regulated pollutants, we need instruments that can detect the nature of the BVOCs that are emitted, how much is emitted, and what happens to them after they are emitted. To meet this need, we designed and built a sampling system that concentrates the BVOCs from the air, and then injects them into a set of capillary columns that separates each of the many different compounds into separate "bands" that elute from the column. The eluting bands are then quantitatively measured using a flame ionization detector. The instrument that was built was deployed at the University of Michigan Biological Station in the summer of 2012. A photograph of the instrument is shown in the attached slide #1. We also built a calibration system, which is used to make sure that the measurements made with the instruments are quantitatively reliable. A photograph of the calibration is shown in the attached slide #2. We then deployed this instrument successfully in a large collaborative field campaign in Alabama in the summer of 2013, and it produced very valuable measurement data on the role of BVOCs in the composition of the atmosphere in the southeastern U.S. Overall, this was a very successful project.
