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Aerosols generated in the Institute for Clean Energy (ICET) High-Efficiency Particulate Air (HEPA) filter test stand become charged due to triboelectric processes during production. High-activity beta sources are used to generate ion pairs within the HEPA test stand. The generated ion pairs bind with aerosols to effectively neutralize surface charges on the aerosols. Several methods to calculate the ion pair concentration within the HEPA test stand are described. Several buildings at Oak Ridge National Lab (ORNL) have been slated for decontamination and decommissioning. Contaminating isotopes must be identified and located. Systematic surveys using gamma-ray scintillation detectors can be used to locate and identify gamma-emitting isotopes. Discussed are methods that use gamma-ray spectroscopy data collected during surveys to locate, identify, determine source strength and corresponding dose rates. Survey data are then used to construct radiation intensity and dose rate maps of the interior of the surveyed structures.

Page 7 was mistyped as being page 8. All content present is in logical order. / A simple method for computing the effect of atmospheric aerosol on the net solar radiation balance of the surface-lower atmosphere system is presented. It was found that in clear sky conditions at Goose Bay, Toronto and Winnipeg, for the period 1977 -1982, the presence of aerosol made the systems 10 -20% more efficient at absorbing radiation than if the aerosol was absent. Furthermore, surface albedo is shown to be the most important parameter governing the effect of aerosol on the net solar radiation balance in an aerosol system, while the effect of volcanic aerosol produced by El Chichon had a minor influence on the net solar radiation balance. / Thesis / Bachelor of Science (BSc)

This thesis presents new insights into the chemical composition of semi-volatile compounds in aerosol samples collected in the central Arctic Ocean close to the North Pole in September 2018. The central Arctic Ocean is an inaccessible location due to the lack of land areas along with heavy pack ice conditions. Therefore, large knowledge gaps remain to understand the Arctic climate system, and in particular the role of aerosol particles in its pristine atmosphere. The chemical composition of the aerosol samples was analysed on a molecular level using High Resolution Time-of-Flight Chemical Ionization Mass Spectrometry coupled to a Filter Inlet for Gases and AEROsols (FIGAERO-HRToF-CIMS). The analysis revealed a significant signal from compounds that are likely from marine sources. One important precursor for marine aerosols is dimethyl sulfide (DMS), a gas released by phytoplankton and ice algae in the Arctic Ocean. DMS oxidises in the atmosphere to produce oxidation products that can contribute to aerosol growth. Analysis of air mass origin with backward trajectories showed that the highest ambient DMS concentrations originated from marine areas around the pack ice. However, no correlation could be shown within the pack ice between ambient DMS and its oxidation product methanesulfonic acid (MSA) in the particle phase. As FIGAERO-HRToF-CIMS is commonly used in areas with higher particle concentrations and has never been used in the central Arctic before, this thesis further demonstrates its suitability for measurements of aerosol chemical composition in this remote region. / Denna avhandling ämnar att presentera nya kunskaper om den kemiska sammansättningen av halvflyktiga föreningar i aerosolprover som samlades in i Norra ishavet nära Nordpolen i september 2018. Den innersta delen av Norra ishavet är svårtillgängligt på grund av bristen på fasta landområden ihop med kompakt packis. Därför kvarstår stora kunskapsluckor i förståelsen av klimatsystemet i Arktis, och i synnerhet aerosolpartiklars roll i dess orörda atmosfär. Den kemiska sammansättningen av aerosolproverna analyserades på molekylnivå med högupplöst kemisk joniseringsmasspektrometri kopplad till ett filterinsläpp för gaser och aerosoler (FIGAERO-HRToF-CIMS). Analysen visade på en tydlig signal från föreningar som sannolikt har marina källor. En viktig kemisk föregångare till marina aerosoler är dimetylsulfid (DMS), en gas som frigörs av fytoplankton och isalger i Ishavet. DMS oxiderar i atmosfären till oxidationsprodukter som kan bidra till en storleksökning av aerosoler. Genom analys av provluftens ursprung med trajektorieanalys visades att de högsta DMS-koncentrationerna kom från havsområdena runt packisen. Ingen korrelation kunde emellertid visas inom packisområdet mellan DMS i gasfas och dess oxidationsprodukt metansulfonsyra (MSA) i partikelfas. Eftersom FIGAERO-HRToF-CIMS ofta används i områden med högre partikelkoncentrationer och aldrig har använts i de inre delarna av Arktis tidigare, visar denna avhandling även att tekniken är lämplig för att mäta den kemiska sammansättningen av aerosoler i detta avlägsna polarområde.

This research explores the role that radical-molecule complexes play in the chemistry of Earth's atmosphere. The formation of such complexes can have direct and pronounced effects on the reaction and product outcome of atmospheric chemical reactions. Some attention is also given to the formation of radial-radical pre-reactive complexes in the HO + ClO system. Peroxy radicals (RO2) can form stable complexes with polar compounds such as H2O, NH3, and CH3OH. For the simplest RO2 radical, HO2, complex formation (e.g., HO2-H2O, HO2-NH3, and HO2-722;CH3OH) gives rise to a significant increase in the HO2 self-reaction rate constant. Although this phenomenon has been observed since the mid-1970s, no satisfactory explanation has been put forward to explain this effect. Herein a rationale for the enhancement of the HO2 self-reaction is given based on extensive geometric, mechanistic and natural bond orbital (NBO) analyses. The apparent lack of a rate enhancement for the methyl peroxy (CH3O2) self-reaction is also presented. The combined insights gained from these two systems are then extended to predict if a water enhancement is expected for the 2-hydroxyethyl peroxy (HOCH2CH2O2) self-reaction kinetics. The computational results of this study are then compared to experimental work and conclusions are drawn towards a general procedure to predict the presence/absence of water initiated rate enhancements in RO2 systems as a whole. Original work regarding the formation of a series of organic RO2-H2O complexes is presented. This work established the effects of different functional groups on the stability of organic peroxy radicals and makes estimates of the associated atmospheric lifetimes and equilibrium constants. This work is further extended to the family of peroxy radicals that form from the atmospheric oxidation of isoprene (the most abundant non-methane biologically emitted hydrocarbon). For the first time, complexes of isoprene peroxy radicals with water are presented along with atmospheric lifetime estimates. Conclusions are made as to the effect of water on the product branching ratio of the isoprene peroxy radical + NO2. The oxidation of hexanal to form hexanal peroxy radicals is discussed within the context of the formation of hexanal peroxy water complexes.Aerosol formation is also perturbed as a result of complexation. Aerosol formation under atmospheric conditions is hypothesized to be initiated by radical-molecule complex formation. For example, in the absence of ammonia, the nucleation of H2SO4 in water vapor to form sulfuric acid aerosols is slow. However, as the concentration of NH3 rises, a marked increase in the rate of sulfuric acid aerosol formation is observed. This work explores the effects of the photolysis products of NH3 (NH2 and NH) on the rate of aerosol formation in systems involving H2SO4, HNO3, HC(O)OH, and CH3C(O)OH. With the exception of H2SO4-NH3 and HNO3-NH3 (geometries already published in the literature), minimum energy structures are presented here for the first time for each of the acid-NHx complexes. Thermochemical data and lifetime estimates are provided for each complex. Conclusions about the relevance of acid-NH2 and acid-NH in the formation of atmospheric aerosols are set forth. Finally, mechanistic insights into the reaction of the hydroxyl radical (OH) and Cl2O are obtained via analysis of the two potential energy surfaces that both involve the formation of HO-Cl2O pre-reactive complexes.

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