Background

The Program for Research on Oxidants: PHotochemistry, Emissions, and Transport (PROPHET) was created in 1996, as a coordinated research effort aimed at investigation of the relationships between atmospheric odd nitrogen, ozone, and forest-atmosphere interactions.  The motivating science questions for PROPHET are described below. 

• How well do we understand the relationships between nitrogen oxides concentrations and ozone production efficiency in the midwest?
• Do we understand the partitioning of nitrogen, and are there missing or uncharacterized atmospheric nitrogen sinks?
• How well do we understand the role of biogenic volatile organic compounds (BVOCs) with respect to ozone formation, and atmospheric nitrogen sequestration?
• What is the impact of ozone deposition on forest productivity?
• Do we understand the environmental controls on BVOC emissions, and can they be adequately simulated?

In the summers of 1997, 1998, and 2000, measurement intensives were conducted to explore our understanding of the relationships between forest-generated volatile organic compounds, atmospheric nitrogen processing, and ozone and other oxidants. These studies involved collaborations among researchers from more than 15 universities and other labs.  Results from some of those studies were published in a PROPHET special section of JGR-Atmospheres, in the October 27, 2001 issue.

Research at the UMBS PROPHET lab and the Ameriflux tower has continued, focusing on atmosphere-canopy interactions. The original focus of the PROPHET studies was on the processing of atmospheric nitrogen, the extent to which we could achieve closure on the nitrogen speciation, and the role of biogenic emissions in processing atmospheric nitrogen. As discussed, e.g. in Thornberry et al. (2001), and Cooper et al. (2001), we have established a reasonably solid understanding of the local and synoptic scale meteorology influencing ozone and nitrogen oxides at the PROPHET site, as well as the distribution and chemistry of the odd nitrogen species. Over the past several years, the PROPHET science team has developed an interest in and plan for effective utilization of the PROPHET infrastructure and science team expertise to study the role of atmospheric deposition of nitrogen, and canopy utilization of atmospheric nitrogen, on carbon sequestration in this type of terrestrial ecosystem. We have developed a separate PROPHET activity, the Biosphere Exchange of Atmospheric Carbon and Odd Nitrogen (BEACON) project. The general objective of BEACON is to develop a quantitative understanding of the impact of atmospheric nitrogen inputs to the forest on carbon utilization and sequestration.  In the short term, we are planning a series of experiments aimed at measurements of fluxes of all important odd-nitrogen species to(/from) the forest canopy, as well as experiments aimed at study of utilization/uptake of nitrogen species at the leaf level.  The specifics of the BEACON project are discussed at http://aoss.engin.umich.edu/PROPHET/Vision/BEACON%20Vision.htm.

BEACON activities will be funded as the individual PROPHET activities, i.e. largely through single-investigator grants.  We anticipate BEACON activities to be ongoing each year, focusing on the growing season, and in association with the IGERT BART program (http://www.bart-wmich.org/).  While BEACON activities will focus directly on forest-atmosphere interactions, PROPHET activities will continue in parallel.  Ongoing PROPHET activities are likely to take advantage of the well characterized VOC/NO_x/free radical chemistry, as well as synoptic and boundary layer meteorology at the PROPHET tower site, and the analytical chemistry and modeling capabilities of the PROPHET science team.  We anticipate continued utilization of the PROPHET tower lab. facility for nitrogen and VOC measurement intercomparison studies, as well as PI-initiated exploratory studies of tropospheric photochemistry in a well-characterized forest environment. Outstanding research questions for PROPHET include:

• What is the role of BVOCs other than isoprene in oxidant chemistry in this type of environment?
• What role do the local BVOCs play in particle generation?
• Are organic nitrates other than those produced from isoprene oxidation important to local scale atmospheric nitrogen sequestration and the nitrogen distribution?
• How will climate change influence the role of atmosphere-forest interactions in regional ozone?
• Do canopy surface processes influence the chemical composition and photochemistry in the boundary layer?