Disjunct Eddy Accumulation Measurements of Organic Nitrate Fluxes Over a Forest Site in Northern Michigan

Fluxes of organic nitrates have been measured at the PROPHET tower site in northern Michigan by the technique of disjunct eddy accumulation (DEA). This relatively new method involves conditional sampling into up and down cartridge-based reservoirs, from a disjunct sample container. In this experiment, air parcels containing target species were sampled at rates proportional to the magnitude and direction of the vertical wind vector. One disjunct sample was taken every 30 seconds by drawing ambient air into analysis tubes containing a sorbent material (Tenax-TA) for a period of one hour. These sorbet tubes were then analyzed by thermal desorption/GC-ECD. The performance of the DEA instrument and GC during their first field deployment is evaluated and the overall flux for several organic nitrate molecules will be reported. Using these data and the gas phase concentrations, dry deposition velocities of these organic nitrates can be calculated and will be discussed here. The potential role and relative importance (compared to other sources of nitrogen) of these molecules in biosphere-atmosphere exchange within a nitrogen limited forest will also be discussed.