Ozone (O₃) and terpenoids react to produce secondary organic aerosol (SOA). This work explored novel ways that these reactions form SOA indoors, with five investigations, in two categories: investigations of (i) the impacts of particle controls on indoor SOA formation, and (ii) two fundamental aspects of indoor SOA formation. For category (i), two investigations examined the particle control devices of ion generators, which are air purifiers that are ineffective at removing particles and emit ozone during operation. With a terpenoid source present (an air freshener), ion generators acted as steady-state SOA generators, both in a 15 m³ chamber and 27 m³ room. The final investigation in category (i) modeled how heating, ventilating, and air-conditioning (HVAC) systems influence SOA formation. Influential HVAC parameters were flow rates, particle filtration, and indoor temperature for residential and commercial models, as well as ozone removal by particle-laden filters for the commercial model. For category (ii), the first investigation measured SOA formation from ozone reactions with single terpenoids and terpenoid mixtures in a 90 L Teflon-film chamber, at low and high ozone concentrations. For low ozone, experiments with only d-limonene yielded the largest SOA number formation, relative to other mixtures, some of which had three times the effective amount of reactive terpenoids. This trend was not observed for high ozone experiments, and these results imply that ozone-limited reactions with d-limonene form byproducts with high nucleation potential. The second investigation in category (ii) explored SOA formation from ozone reactions with surface-adsorbed terpenoids. A model framework was developed to describe SOA formation due to ozone/terpenoid surface reactions, and experiments in a 283 L chamber determined the SOA yield for ozone/d-limonene surface reactions. The observed molar yields were 0.14–0.16 over a range of relative humidities, and lower relative humidity led to higher SOA number formation from surface reactions. Building materials on which ozone/d-limonene surface reactions are predicted to lead to substantial SOA formation are those with initially low surface reactivity, such as glass, sealed materials, or metals. The results from category (ii) suggest significant, previously unexplored mechanisms of SOA number formation indoors. / text

Aromatic hydrocarbons constitute an important fraction (~20%) of total volatile organic compounds (VOCs) in the urban atmosphere. A better understanding of the aromatic oxidation and its association in urban and regional ozone and organic aerosol formation is essential to assess the urban air pollution. This dissertation consists of two parts: (1) theoretical investigation of the toluene oxidation initiated by OH radical using quantum chemical and kinetic calculations to understand the mechanism of O3 and SOA precursors and (2) experimental investigation of atmospheric new particle formation from aromatic acids. Density functional theory (DFT) and ab initio multiconfigurational calculations have been performed to investigate the OH-toluene reaction. The branching ratios of OH addition to ortho, para, meta, and ipso positions are predicted to be 0.52, 0.34, 0.11, and 0.03, respectively, significantly different from a recent theoretical study of the same reaction system. Aromatic peroxy radicals arising from initial OH and subsequent O2 additions to the toluene ring are shown to cyclize to form bicyclic radicals rather than undergoing reaction with NO under atmospheric conditions.Isomerization of bicyclic radicals to more stable epoxide radicals possesses significantly higher barriers and hence has slower rates than O2 addition to form bicyclic peroxy radicals. At each OH attachment site, only one isomeric pathway via the bicyclic peroxy radical is accessible to lead to ring cleavage. Decomposition of the bicyclic alkoxy radicals leads primarily to formation of glyoxal and methyl glyoxal along with other dicarbonyl compounds. Atmospheric aerosols often contain a considerable fraction of organic matter, but the role of organic compounds in new nanometer-sized particle formation is highly uncertain. Laboratory experiments show that nucleation of sulfuric acid is considerably enhanced in the presence of aromatic acids. Theoretical calculations identify the formation of an unusually stable aromatic acid-sulfuric acid complex, which likely leads to a reduced nucleation barrier. The results imply that the interaction between organic and sulfuric acids promotes efficient formation of organic and sulfate aerosols in the polluted atmosphere because of emissions from burning of fossil fuels, which strongly impact human health and global climate.

<p>  </p> <p>Secondary organic aerosols (SOA) play an important role in the Earth’s radiative budget due to their potential to either warm or cool the atmosphere through light absorption or light scattering, respectively, and to cool or warm the lower atmosphere by acting as cloud condensation nuclei. SOA are air-suspended liquid and semi-solid droplets that form through multiphase chemical processes. Atmospheric photochemical oxidation of volatile organic compounds (VOCs) in the presence of air pollutants, such as NO_x (NO + NO₂) and the OH radical, promote formation of low volatility organic products that eventually condense to form SOA. To better understand the sources and sinks, formation, and fate of SOA, laboratory studies investigating oxidation of a biogenic VOC as well as anthropogenic emissions of SOA precursors were conducted. The first study (<em>Chapter 3</em>) investigated the OH-initiated oxidation of β-ocimene, a biogenic volatile organic compound (BVOC) released from vegetation, including forests, agricultural landscapes, and grasslands emitted during the daytime. The oxidation of BVOCs in the presence of NO_x leads to the formation of functionalized organic nitrate (RONO₂) compounds and isomers that easily condense to form SOA. To understand their atmospheric fate, the RONO₂ hydrolysis rate constants were quantified and found to be highly pH dependent. The findings of this study provide key insights into the formation and fate of organic nitrates and NO_x cycling in forested environments from daytime monoterpenes that were not previously included in atmospheric models. </p> <p>The second study (<em>Chapters 4 and 5</em>) investigated condensed waste emissions generated during Cured-In-Place-Pipe (CIPP) installations. This installation process is the most popular, least expensive, and most frequently used technology that cures leaking sanitary and stormwater sewers. Waste plumes discharged during pipe manufacture are complex multi-phase mixtures of volatile and semi-volatile organic compounds (VOC and SVOC, respectively), primary organic aerosols and SOA, fine debris of partially cured resin, and direct emission of nanoplastic particles that are all blown into the atmospheric environment at significant concentrations at worksites. This work unveiled a direct emission source of airborne nanoplastic particles as well as substantial concentrations of hazardous compounds and SOA precursors that were previously unrecognized. </p>