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Eddy-covariance observations of the atmosphere-biosphere exchange of nitrogen oxides


Oxidative forms of reactive nitrogen (NOy) impact air quality, nutrient dynamics, and climate. Our understanding of the sources and sinks of atmospheric NOy that result from exchange between the atmosphere and biosphere is poorly constrained due to the lack of adequate instrumentation.

In this dissertation, I apply novel technologies to the question of NOy exchange and describe observations of fluxes at the atmosphere-forest interface. I use thermal-dissociation laser-induced fluorescence, chemiluminescence, and the micrometeorological eddy-covariance method. Simultaneous observations of the rate and magnitude of exchanges and vertically resolved concentration measurements of the NOy species (NO, NO2, RO2NO2, RONO2 and HNO3) were measured in addition to a wide suite of relevant parameters including canopy structures, meteorological parameters, and associated chemical species as part of the Biosphere Effects on AeRosols and Photochemistry EXperiment (BEARPEX), which took place June 15 - July 31, 2009 at a Ponderosa pine plantation on the western slope of Sierra Nevada Mountains in California.

I present observational evidence for active within canopy chemistry resulting in simultaneous production and removal of NOX within a forest canopy. My observations provide direct evidence for a NOX canopy reduction factor and for an NO2 compensation point. I also establish that an unusual peroxynitrate is formed within the canopy and then emitted to the atmosphere above underscoring the importance of coupling between biogenic volatile organic compounds and NOX to the fluxes of NOX, NOy and BVOC.

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