Collaborative Research: Determination of Nitrous Acid and Nitrogen Dioxide Flux and Concentration Over Forest Canopies Using Quantum Cascade Laser Absorption Spectroscopy

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The production and loss mechanisms, and the magnitude of nitrous acid (HONO) fluxes to the atmosphere, will be investigated by constructing improved instrumentation capable of fast response measurements suitable for eddy-covariance flux, and by deploying the new sensor to field test it by making detailed measurements of HONO concentrations and fluxes and their covariance with other nitrogen oxides, oxidants, and environmental conditions. Photolysis of nitrous acid (HONO) is a major source of OH radicals in the boundary layer but poorly understood. The PI's will (1) construct and test a 2-channel Quantum-Cascade laser absorption spectrometer (QCLAS) capable of high frequency measurement of HONO and NO2, (2) measure HONO, NO, NO2, and NOy at a suburban site influenced by vehicle emissions, and above a forest canopy at a rural site, and (3) interpret the concentration and flux observations within a photochemical model framework, based on GEOS-Chem, to provide new insights into the processes controlling HONO in the boundary layer. These research activities will enhance existing research infrastructure by providing instrument development and supporting research partnerships. The instrument addresses a critical societal need for a reliable fast-response instrument to measure HONO in continuous operation to assess pollution impacts. The HONO-NO2 QCLAS will enable participation in a variety of future field measurement campaigns to examine HONO production and loss. This work will directly support a graduate-student thesis project and will serve as a research topic for two undergraduate students and a high school teacher at the Harvard Forest LTER as part of Research Experience for Undergraduates (REU) program and Research Experience for Teachers (RET) summer programs.