Date of Award

1-1-2011

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School/Department

Department of Environmental Health Sciences

Content Description

1 online resource (xvi, 297 pages) : illustrations (some color)

Dissertation/Thesis Chair

Xianliang Zhou

Committee Members

James Schwab, Lei Zhu, Kevin Civerolo, James Webber

Keywords

1-D model, HONO, nitric acid, photolysis, re-NOx-ification, surface, Nitric acid, Photochemistry, Tropospheric chemistry

Subject Categories

Atmospheric Sciences | Environmental Sciences | Other Chemistry

Abstract

The reactive nitrogen trace gases (NOy) including nitrogen oxides (NOx) and their secondary products are known to cause ground-level ozone pollution, photochemical smog, acid deposition, and overall air quality degradation. NOx was believed to be permanently removed from the atmospheric by HNO3 formation and deposition. However, our laboratory experimental results show that HNO3 can be remobilized back to photochemically labile HONO and NOx (re-NOx-ification). We have verified and quantified HONO and NOx production from the photolysis of HNO3 on various surfaces, including Pyrex, leaves of plants, and other environmentally relevant materials, under the radiation of natural sunlight or an artificial light (λ ≥ 290 nm). The photolysis rates are normalized to clear sky tropical noontime conditions. On Pyrex surfaces, the average photolysis rate constant for adsorbed HNO3, in terms of HONO and NOx production, is (2.5 ± 0.6) ×10-5 s-1, with a HONO/NOx ratio of 0.72. The average photolysis rate constant of HNO3 is (3.4 ±1.8) ×10-5 s-1 on plant leaf surfaces, with HONO/NOx ratio of 2.8, and is (2.6 ±1.3) ×10-5 s-1 on other environmental surfaces, with a HONO/NOx ratio of 1.6. The HNO3 photolysis rate constants on surfaces are 1-2 orders of magnitude higher than those in the gas and aqueous phases. To evaluate the importance of this surface photolytic process as a HONO source and as a potential re-NOx-ification pathway, a 1-D model has been developed, by coupling the Regional Atmospheric Chemical Mechanism (RACM) with vertical transport and surface chemistry. The HONO sources include the dark heterogeneous source, photo-excited NO2-5 hydrolysis, in situ photolytic source, and the surface HNO3 photolysis. The relative importance of these HONO sources has been compared. Performance evaluation and sensitivity test have been carried out for the 1-D model. The model has successfully predicted typical summer diurnal HONO variation, and showed that photolysis of HNO3 on surface accounts for over 60% of observed midday HONO budget. The in situ photolytic HONO source accounts for 70% of midday HONO budget in the mixed layer. The results have indicated that the HNO3 photolysis on surfaces is an important re-NOx-ification process, resulting in higher photooxidants concentrations including O3, and OH.

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