Measurements of OH and HONO in an Indiana Forest
Abstract
As the dominant oxidant in the atmosphere, the hydroxyl radical (OH) plays a vital role in many atmospheric processes. OH reacts with volatile organic compounds (VOCs), and in the presence of nitrogen dioxides (NOx) causes an increase in the concentration of ozone. The oxidation of VOCs reduces their volatility, which increases partitioning into the particle phase and results in the formation and growth of aerosols. Previous measurements and modeling studies have shown some discrepancies in the sources of OH, particularly with respect to the importance of nitrous acid (HONO) photolysis. HONO is produced through homogeneous and heterogeneous chemical processes involving nitrogen oxides as well as combustion emissions, leading to high concentrations in urban environments. It is also a product of some bacterial pathways and surface reactions, resulting in lower ambient concentrations in remote areas.
OH and HONO were measured during the summer of 2019 at the Indiana University Research and Teaching Preserve field laboratory — a high-isoprene, low-NOx forested site located near the Indiana University Bloomington campus. A laser photofragmentation laser-induced fluorescence (LP-LIF) instrument was used to measure both species. OH was measured using the Laser-Induced Fluorescence Fluorescence Assay by Gas Expansion (LIF-FAGE) technique. An additional laser is used to photolyze HONO into OH for subsequent detection by LIF. Supporting measurements of NOx, ozone, VOCs, and meteorological data were collected and used to constrain 0-dimensional box models based on the Regional Atmospheric Chemistry Mechanism (RACM2) and the Master Chemical Mechanism (MCM) in order to reproduce the observed OH and HONO concentrations as well as the OH/HONO ratio in order to gain insight into the sources of HONO in this environment.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A11K2688R
- Keywords:
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- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0312 Air/sea constituent fluxes;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0317 Chemical kinetic and photochemical properties;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0341 Middle atmosphere: constituent transport and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE