Investigation of the Photoenhanced Reduction of Nitrogen Dioxide (NO2) on Organic Films and Above Soils as the Missing Source of Daytime Tropospheric Nitrous Acid (HONO)

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dc.contributor.advisorHarris, Geoffrey
dc.creatorWall, Kristin
dc.date.accessioned2015-01-26T14:11:54Z
dc.date.available2015-01-26T14:11:54Z
dc.date.copyright2013-06-14
dc.date.issued2015-01-26
dc.date.updated2015-01-26T14:11:54Z
dc.degree.disciplineChemistry
dc.degree.levelDoctoral
dc.degree.namePhD - Doctor of Philosophy
dc.description.abstractRecent observed unpredictably high HONO daytime concentrations, demanding its ordinarily proposed heterogeneous source to proceed > 60 times faster at noon than during the night, prompted this study, concerning the effect of UV-A radiation on the uptake kinetics of gas-phase NO2 on various phenolic-containing organic films using a wetted-wall flow tube (WWFT) photoreactor. Experimental methods are discussed in detail. A time-dependent model for non-equilibrium conditions incorporating both the chemistry and diffusion for predicting a best-fit reaction probability, ɣbest-fit, as a function of the experimental parameters is detailed. Emphasis is placed on the kinetics of the photoenhanced NO2 uptake reaction under acidic conditions for humic acids (HA), a ubiquitous group of environmental compounds. The linear correlation of HONO production rate with [NO2]0 (k1 = 6.7×10-3 s-1) for commercial HA suggest NO2- particles only diffuse throughout the surface layer depth, as experimentally verified. In general, the pH-dependent results were qualitatively coherent with those of Stemmler et al. (2006), monitoring increases in the photoenhanced HONO formation with pH, owing to increases in reactivity in the reaction with NO2 with several carboxyl groups within the commercial HA with deprotonation, however centred on more authentic pH conditions of anaerobic humic soils (between pH 1.5 and 4.3). A value of krxn = 2.70×10-3 s-1 at pH 3 was obtained, indicative that there was no competition with the hydrolysis reaction, for the tested conditions. Assuming that ɣrxn was rate-limiting, ɣdiffusion was estimated to account for ~ 19% of the total uptake, consistent with the model results. The humification-generated bacteria likely functioned as multicellular aggregates on the acidic HA substrate, producing a biofilm containing numerous chromophoric sensitizer units capable of photochemically reducing NO2 to HONO, defending the observed exponential dependence of HONO yield on irradiance under the tested conditions. The datasets presented for the photoenhanced reaction of NO2 on acidic HA films provide a rather complete kinetic ‘picture’ of an important surface reaction (ɣbest-fit, max of 10-8 at pH 4 under the tested conditions). The scaling up assessments of the kinetic results for the small-scale photoreactor to that of both urban and rural scales are discussed.
dc.identifier.urihttp://hdl.handle.net/10315/28171
dc.language.isoen
dc.rightsAuthor owns copyright, except where explicitly noted. Please contact the author directly with licensing requests.
dc.subjectChemistry
dc.subjectPhysical chemistry
dc.subjectAtmospheric chemistry
dc.subject.keywordsScaling up assessments (urban/rural scales)en_US
dc.subject.keywordsNitrogen dioxideen_US
dc.subject.keywordsNitrous aciden_US
dc.subject.keywordsOrtho-nitrophenolsen_US
dc.subject.keywordsHumic aciden_US
dc.subject.keywordsPhotosensitized electron transferen_US
dc.subject.keywordsWetted-wall flow tube photoreactoren_US
dc.subject.keywordsFlow dynamicsen_US
dc.subject.keywordsTime-dependent non-equilibrium modelen_US
dc.subject.keywordsPartitioning of total uptake producten_US
dc.subject.keywordsReaction probabilityen_US
dc.subject.keywordsDiffusionen_US
dc.subject.keywordsSurface layer reactionen_US
dc.subject.keywordsDeprotonationen_US
dc.subject.keywordsAnaerobic conditionsen_US
dc.subject.keywordsHumification-generated bacteriaen_US
dc.subject.keywordsBiofilmen_US
dc.subject.keywordsIrradianceen_US
dc.titleInvestigation of the Photoenhanced Reduction of Nitrogen Dioxide (NO2) on Organic Films and Above Soils as the Missing Source of Daytime Tropospheric Nitrous Acid (HONO)
dc.typeElectronic Thesis or Dissertation

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