<p> Nitrous acid (HONO) is a photochemical source of hydroxyl radical that plays an important role in initiating radical reactions leading to photochemical air pollution and aerosol formation in the lower atmosphere. Field studies suggest nocturnal and daytime HONO sources that stem from heterogeneous reactions on environmental surfaces. However, the mechanisms are not well-understood and atmospheric models under-predict daytime HONO levels by 30–50%. The main aim of this research is to examine proposed nocturnal and daytime sources with a focus on elucidating the mechanisms of HONO formation and understanding the variables controlling this important process. Results from four projects are presented. The first project focuses on aqueous nitrate (<sub>3</sub><sup> –</sup>) photolysis and the role that nitrogen dioxide (NO<sub>2</sub>) hydrolysis plays in the formation process. The second involves linking the flux of HONO from agricultural and urban soil samples to ammonia oxidizing bacteria and archaea. The third project elucidates the mechanism of NO<sub>2</sub> reduction on surfaces containing humic acids (HA), specifically focusing on quinone and hydroquinone redox chemistry. The fourth project seeks to explain how nitrate photolysis on HA or iron surfaces can be an important daytime source of HONO. We suggest that NO<sub>3</sub><sup>–</sup> photolysis in the presence of chromophoric compounds and OH radical scavengers, which are naturally present on the environment surfaces, help explain the higher than expected daytime HONO levels observed during recent field studies. </p>
| Identifer | oai:union.ndltd.org:PROQUEST/oai:pqdtoai.proquest.com:10196158 |
| Date | 14 December 2016 |
| Creators | Scharko, Nicole K. |
| Publisher | Indiana University |
| Source Sets | ProQuest.com |
| Language | English |
| Detected Language | English |
| Type | thesis |
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