Date of Award




Document Type

Master's Thesis

Degree Name

Master of Science (MS)


Department of Environmental Health Sciences

Content Description

1 online resource (vi, 61 pages) : color illustrations, color maps.

Dissertation/Thesis Chair

Xianliang Zhou

Committee Members

Haider Khwaja, Ying Wang


Nitrous acid, Nitrogen oxides, Atmospheric nitrous oxide, Tropospheric chemistry, Nitrous Acid, Nitrogen Oxides

Subject Categories

Other Chemistry


Nitrous acid (HONO) is an important reactive nitrogen species and a precursor to the hydroxyl radical. It plays important roles in reactive nitrogen recycling and in photo-oxidant formation in the troposphere. However, much is still unknown about its formation mechanisms and distributions in the troposphere. This research is part of NOMADSS (Nitrogen, Oxidants, Mercury, and Aerosol Distributions, Sources and Sinks) field study contributed by over 10 research groups in the United States to investigate the tropospheric chemistry of reactive nitrogen, mercury, oxidant and aerosols. One of the goals was to study the HONO distribution and formation mechanisms in the troposphere. The observed HONO mixing ratios ranged from low ppt levels in the background ambient air to 70 ppt in biomass burning plumes in the free troposphere, and from 6 to 20 ppt in the background boundary layer, to a maximum of 82 ppt in power plant plumes. HONO sources and sinks are analyzed, and three cases in different atmospheres were studied: clean marine air, background continental ambient air, and power plant plumes. Photolysis is the dominant HONO sink throughout the troposphere during the day; particulate nitrate photolysis is the main HONO source in clean marine air and in the background continental air, while NOx is the dominant HONO precursor via its gas-phase and heterogeneous reactions within the industrial plumes. No significant nighttime accumulation of HONO was observed in the air mass isolated from ground surface. The conclusion from this study is that photolysis of particulate nitrate is a major daytime source of HONO in the low-NOx troposphere and is an important pathway to recycle HNO3/nitrate back to photochemically reactive NOx (re-NOx¬-ification).