Fog has broad impacts on transportation safety, agricultural production, drought resilience, and climate. The frequency of wintertime radiation fog in valleys throughout the world has been changing over the past century. This dissertation focuses on understanding the drivers of fog trends observed in California’s Central Valley and Italy’s Po Valley, specifically investigating the competing effects of warming climate versus air pollution controls in the twentieth and early twenty-first century.

Beginning in the Central Valley, this dissertation finds that dense fog frequency (visibility < 400 meters) increased 85% from 1930-1970, then declined 76% in the last 36 winters. Throughout these changes, fog frequency exhibited a consistent north-south trend, with maxima in southern latitudes. I analyzed seven decades of meteorological data and five decades of air pollution data to determine the most likely drivers changing fog, including temperature, dew point depression, precipitation, wind speed, and NOx (oxides of nitrogen) concentration. Climate variables, most critically dew point depression (DPD), strongly influence the short-term (daily to annual) variability in fog frequency; however, the frequency of optimal conditions for fog formation show no observable long-term trend from 1980 to 2016. NOx concentration, which is a limiting precursor to the ammonium nitrate aerosol that dominates wintertime particulate matter in the valley, has an increasing north-south concentration gradient, consistent with the gradient in fog frequency. NOx declined continuously over this period, also consistent with the long-term temporal and spatial trends in fog. As development in the Central Valley increased direct particle and other pollutant emissions from 1930-1970, fog frequency increased. Following the Clean Air Act, particle emissions quickly declined, and NOx emissions declined steadily, reducing the cloud condensation nuclei (CCN) available for fog formation. I conclude that while the short-term fog variability is dominantly driven by climate fluctuations, the longer-term temporal and spatial changes in fog have been driven by changes in air pollution. For conditions close to the dew point, a decrease in fog of 5 days per year per 10 ppb NOx decrease occurred across the Central Valley.

To further understand the multivariate, nonlinear contributors to fog formation, this dissertation used generalized additive models to identify the relative significance of climate and air pollution variables affecting visibility, an indicator of dense fog, and compare the drivers changing fog in the Central Valley to Italy’s Po Valley, which saw a 50% decline in fog frequency since 1980. Effective regulatory strategies in the Po Valley have also resulted in stark reductions in inorganic pollution emissions, thus reducing the CCN available for fog formation. Over 56-65% of the variance in visibility is consistently explained by variability in DPD, pollution concentration, wind speed, and precipitation. Variability in DPD, which incorporates both water availability and temperature, has the most pronounced influence on daily time scales, but shows no substantial long-term trends in time over the observation period. The variability in NOx concentration explains 33-70% of the variance in visibility (depending on the site) when investigating days with average DPD < 3.5℃. This suggests that fog frequency is specifically sensitive to fluctuations in CCN number concentration when meteorological conditions are favorable to fog formation (e.g. when DPD is low). While DPD is a primary driver of daily variability, the significant influence of NOx concentration on the visibility response suggests that rapid pollution declines in both valleys have had an important impact on the diminished fog season since 1980. This demonstrates that the regulatory measures that mitigate pollution concentration have valuable benefits, not only on the health outcomes of those potentially exposed, but also in reducing the dangerous dense fog frequency that was anthropogenically enhanced with industrialization.

To further understand the safety implications of reductions in air pollution and fog events, I analyzed a 20-year record of fog-related accidents in the Central Valley (1996-2016). Decades of multicar pile-ups along its highways made the region widely-known for the frequency and severity of its fog-related accidents. Yet, the Central Valley saw a 65% decline in fog-related accidents over 20 winters, the variance of which is best explained by the sharply declining trend in seasonal fog hours over the same period. Annual frequency of fog hours as summarized for each fog season explain an average of ~80% of the annual variability in fog-related accidents in the counties of highest roadway volume, showing that the declining trend in fog is a strong determinant in the declining trend in accidents. The subsequent improvement in visibility results in annual fog-related injuries falling by 72%, with the valley seeing an average of 550 fewer injuries from fog accidents in 2015-2016 than in 1996-1997.

The human safety and commercial benefits to a reduction in fog-accidents and the resulting roadway delays is well documented. The declining trend in dense fog in this region has had a pronounced impact on the declining frequency of fog-related accidents. This dissertation implicates regional air pollution concentration as a critical driver in the long-term trend of fog frequency. The strong link between the historical number of Central Valley fog events and trends in pollution concentration provides a measure of how regulations that led to decreases in aerosol concentration, and thereby wintertime fog frequency, also influenced the declining trend in fog-related accidents.

Methane (CH4) and nitrous oxide (N2O) are two major greenhouse gases that contribute significantly to the increase in anthropogenic radiative-forcing causing perturbations to the earth's climate system. In a watershed moment in the state's history of environmental leadership and commitment, California, in 2006, opted for sharp reductions in their greenhouse gas (GHG) emissions and adopted a long-term approach to address climate change that includes regulation of emissions from individual emitters and source categories. There are large CH4 and N2O emissions sources in the state, predominantly in the agricultural and waste management sector. While these two gases account for < 10% of total annual greenhouse gas emissions of the state, large uncertainties exist in their `bottom-up' accounting in the state GHG inventory. Additionally, an increasing number of `top-down' studies based on ambient observations point towards underestimation of their emissions in the inventory.

Three intensive field observation campaigns that were spatially and temporally diverse took place between 2010 and 2013 in the Central Valley of California where the largest known sources of CH4 and N2O (e.g. agricultural systems and dairies) and potentially significant CH4 sources (e.g. oil and gas extraction) are located. The CalNex (California Nexus - Research at the Nexus of Air Quality and Climate Change) field campaign during summer 2010 (May 15 - June 30) took place in the urban core of Bakersfield in the southern San Joaquin Valley, a city whose economy is built around agriculture and the oil and gas industry. During summer of 2011, airborne measurements were performed over a large spatial domain, all across and around the Central Valley as part of the CABERNET (California Airborne BVOC Emission Research in Natural Ecosystem Transects) study. Next, a one-year continuous field campaign (WGC 2012-13, June 2012 - August 2013) was conducted at the Walnut Grove tall tower near the Sacramento-San Joaquin River Delta in the Central Valley.

Through analysis of these field measurements, this dissertation presents the apportionment of observed CH4 and N2O concentration enhancements into major source categories along with direct emissions estimates from airborne observations. We perform high-precision measurements of greenhouse gases using gas analyzers based on absorption spectroscopy, and other source marker volatile organic compounds (VOCs) using state of the art VOC measurement systems (e.g. proton transfer reaction mass spectrometry). We combine these measurements with a statistical source apportionment technique called positive matrix factorization (PMF) to evaluate and investigate the major local sources of CH4 and N2O during CalNex and Walnut Grove campaigns. In the CABERNET study, we combine measurements with an airborne approach to a well-established micrometeorological technique (eddy-covariance method) to derive CH4 fluxes over different source regions in the Central Valley.

In the CalNex experiments, we demonstrate that dairy and livestock remains the largest source sector of non-CO2 greenhouse gases in the San Joaquin Valley contributing most of the CH4 and much of the measured N2O at Bakersfield. Agriculture is observed to provide another major source of N2O, while vehicle emissions are found to be an insignificant source of N2O, contrary to the current statewide greenhouse gas inventory which includes vehicles as a major source. Our PMF source apportionment also produces an evaporative/fugitive factor but its relative lack of CH4 contributions points to removal processes from vented emissions in the surrounding O&G industry and the overwhelming dominance of the dairy CH4 source.

In the CABERNET experiments, we report enhancements of CH4 from a number of sources spread across the spatial domain of the Central Valley that improves our understanding of their distribution and relative strengths. We observe large enhancements of CH4 mixing ratios over the dairy and feedlot intensive regions of Central Valley corresponding with significant flux estimates that are larger than CH4 emission rates reported in the greenhouse gas inventory. We find evidence of significant CH4 emissions from fugitive and/or vented sources and cogeneration plants in the oil and gas fields of Kern County, all of which are minor to insignificant CH4 sources in the current greenhouse gas inventory. The CABERNET campaign represents the first successful implementation of airborne eddy covariance technique for CH4 flux measurements.

At Walnut Grove, we demonstrate the seasonal and temporal dependence of CH4 and N2O sources in the Central Valley. Applying PMF analysis on seasonal GHG-VOC data sets, we again identify dairies and livestock as the dominant source of CH4. A clear temporal dependence of emissions originating from a wetlands / Delta CH4 source is observed while CH4 contributions are also observed from a source originating from upwind urban and natural gas extraction activities. The agricultural soil management source of N2O has a seasonal dependence coincident with the agricultural growing season (and hence, fertilizer use) accounting for a majority of the N2O enhancements during spring and summers but being reduced to a negligible source during late fall and winters when manure management N2O emissions from dairy and livestock dominate the relative distribution. N2O is absent from the `urban' source, in contrast to the significant contribution to the statewide N2O inventory from vehicle emissions.

The application of greenhouse gas source apportionment using VOC tracers as identification tools at two independent sites in the Central Valley over vastly different temporal resolutions provide significant insights into the regional distribution of major CH4 sources. Direct airborne eddy covariance measurements provide a unique opportunity to constrain CH4 emissions in the Central Valley over regional spatial scales that are not directly observable by ground-based methods. Airborne observations provide identification of `hotspots' and under-inventoried CH4 sources, while airborne eddy covariance enables quantification of emissions from those area sources that are largely composed of arbitrarily located minor point sources (e.g. dairies and oil fields).

The top-down analysis provides confirmation of the dominance of dairy and livestock source for methane emissions in California. Minor but significant contributions to methane emissions are observed from oil and gas extraction, rice cultivation and wetlands; the estimates for these sectors being either negligible (e.g. wetlands) or highly uncertain (e.g. oil and gas extraction) in the statewide inventories and probably underestimated as a proportion of the total inventory. The top-down analysis also confirms agricultural soil management and dairy and livestock as the two principal sources of N2O consistent with the inventory, but shows that N2O contributions attributed to the transportation sector are overestimated in the statewide inventory. These new top down constraints should be used to correct these errors in the current bottom-up inventory, which is a critical step for future assessments of the efficacy of emission reduction regulations. Particularly, measurement techniques like vehicle dynamometer emission calculations (for transportation sources), source-specific short range ground-based inverse dispersion (for dairy and livestock sources), airborne eddy covariance and airborne mass balance approach based emissions estimation (over oil and gas fields) and ground based eddy-covariance (for wetlands and agriculture sector) can be used effectively to generate direct emissions estimates for methane and nitrous oxide that help update and improve the accuracy of the state inventory.

Organic carbon in the atmosphere fuels the formation of ozone and comprises a large fraction of fine particulate matter, both of which are detrimental to human health. Particulate matter additionally is a source of uncertainty in radiative forcing predictions, hindering predictions of climate change impacts. Atmospheric organic carbon is complex, consisting of thousands of different compounds and covering more than 15 orders of magnitude in volatility (vapor pressure) and widely varying chemical reactivity. Many of these compounds serve as specific indicators of pollution sources or atmospheric chemical processes. In this work, two different advanced custom instruments for measurement of speciated volatile, intermediate volatility and semivolatile organic compounds (VOCs, IVOCs and SVOCs) are used to elucidate and profile the sources of pollution in distinct atmospheric environments. One of these instruments is introduced for the first time along with its design and development details.

Chapter 2 presents a suite of semivolatile markers of fresh biomass burning (BB) measured at a rural site in Amazonia, Brazil by the Semivolatile Thermal desorption Aerosol Gas chromatograph (SV-TAG), which specializes in hourly speciated measurements of IVOCs and SVOCs and their partitioning between the gas and particle phases. These 16 markers are found to comprise the majority of fresh BB organic aerosol. Despite much greater concentrations in the dry season versus the wet season, the BB markers comprise about the same fraction of total organic aerosol in both the dry and wet seasons. Composition of individual BB events and atmospherically aged air parcels were highly variable but provide a chemical profile of fresh BB in the Amazon.

By combining traditional speciated VOC measurement instrumentation with the SV-TAG, the Comprehensive Thermal desorption Aerosol Gas chromatograph (cTAG) is sensitive to a wider range of volatility of reactive organic carbon. cTAG joins a layered bed of adsorbents for VOC and IVOC collection and a reusable metal mesh filter for SVOC collection together before a single mass spectrometer, providing consistent quantification across the volatility range. Chapter 3 presents design and development details for cTAG, including VOC and IVOC collector design optimization, performance of a custom liquid evaporation system for VOCs and IVOCs, and verification that ozone removal is effective while not perturbing measured concentrations of nonreactive compounds. Potential applications of this instrument are presented using a brief analysis of field data.

Chapter 4 analyzes major sources of pollution in suburban Livermore, California using measurements of 123 VOCs, IVOCs and SVOCs collected by cTAG. Positive Matrix Factorization on the generated timelines yields 13 distinct factors representing different sources and processes in the atmosphere, including gasoline exhaust, consumer products, biomass burning, secondary oxidation, emissions from evaporative sources and more. Monoterpenoid mass was present in greater quantities in the consumer product factor than biogenic sources, consistent with recent observations in other urban contexts. Several factors contained significant mass from measurements on both channels of cTAG, indicating that the expanded volatility range afforded by cTAG led to more complete chemical characterization of those sources.

The final chapter notes directions for future research and explores measurement and analysis opportunities for cTAG.

Due to a combination of climate change and fire suppression, wildfires are becoming larger and more frequent in the western United States. Biomass burning is the largest global source of carbonaceous particulate matter (PM), and the second largest global source of volatile organic compounds (VOCs) in the atmosphere. Many organic compounds emitted from wildfires have human health impacts, and their atmospheric transformations produce hazardous secondary pollutants. However, there is a lack of comprehensive molecular level characterization of organic compounds in wildfire smoke, due to the chemical complexity and wildfires’ relatively episodic nature. In this work, PM and VOCs in the wildfire smoke from the point of emission to the ambient atmosphere where exposure occurs were examined. The goal is to characterize the compositions of wildfire emissions and aged wildfire smoke, their impact on urban air quality, and how indoor environments are affected by outdoor intrusion of the wildfire particulate matter.

Chapter 1 introduces the background and motivation for this work. It provides a review of current knowledge and identifies knowledge gaps in the atmospheric chemistry of wildfire particulate matter and volatile organic compounds. To elucidate the air quality impact of wildfire smoke, we should first determine the compounds emitted from wildfires. In Chapter 2, as a part of the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) campaign, we had the opportunity to collect fresh western US wildfire smoke samples of gas and particles very close to the fires. The samples were analyzed using two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC ToF-MS) instruments. The modified combustion efficiency (MCE), an indicator of the completeness of combustion, was found to be a good predictor of carbonaceous particulate matter emissions, except elemental carbon. The molecular level analysis reveals high emissions of monoterpenes, diterpenoids and resin acids, probably because of the distillation driven by heat from the fires. The speciated measurements also help to confirm that evaporation of semi-volatile particle phase organic compounds took place in smoke plumes.

We also examined the organic composition of wildfire smoke on the UC Berkeley campus, when smoke from the October 2017 Northern California wildfires (~55-65 km upwind) reached the San Francisco Bay Area. Unlike the FIREX-AQ study which focuses on wildfires in the remote atmosphere, we had a great opportunity to study the interactions between urban pollution and wildfire smoke. In Chapter 3, the composition of volatile organic compounds in smoke plumes measured by proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) is reported. By correlation analysis with known primary and secondary tracers, compounds consumed or formed in the daytime aging of wildfire smoke were identified. It is also demonstrated that the wildfire VOCs added to the organic reactivity in the urban atmosphere and raised the level of ozone in the San Francisco Bay Area. In Chapter 4, the composition of organic particulate matter speciated using the GC×GC HR-ToF-MS is reported. Sugar and sugar derivatives were found to be the most abundant GC-measurable compounds in wildfire plumes, followed by mono-carboxylic acids, aromatic compounds, other oxygenated compounds, and terpenoids. By tracking 572 compounds’ time series using hierarchical analysis, a unique daytime aging factor which consists of oxygenated aromatic compounds and multifunctional acids was identified.

The wildfire particulate matter can also affect the indoor air quality. Previous characterizations of exposure to wildfire smoke particles were based mainly on outdoor concentrations of PM2.5 (particles with aerodynamical diameters < 2.5 µm). Since people mainly shelter indoors during smoke events, the infiltration of wildfire PM2.5 into buildings determines exposure. Chapter 5 presents analysis of infiltration of wildfire PM2.5 into more than 1,400 buildings in California using data from the PurpleAir sensor network. Our study reveals that infiltration of PM2.5 during wildfire days was substantially reduced compared with non-fire days, due to people’s behavioral changes. These results improve understanding of exposure to wildfire particles and facilitate informing the public about effective ways to reduce their exposure.

A summary of the major findings of this work, and recommendations for future research, are presented in the final chapter of this dissertation.

Understanding organic aerosol (OA) sources and secondary OA (SOA) formation is crucial to elucidate their human health and climate change effects, but has been limited by lack of instrumentation capable of in-situ measurements of organic speciation in the atmosphere across the vapor pressure range of semi-volatile organic compounds (SVOCs) and OA. This dissertation describes 1) the development of a novel instrument based on a thermal desorption aerosol gas chromatograph (TAG), called semi-volatile TAG (SV-TAG) which enables quantitative measurements of specific chemical tracers in SVOCs and OA and 2) application of this new instrument to investigate the various source contributions to OA and SOA formation.

The development of the SV-TAG was initiated by employing a denuder difference method to improve the capability of the TAG for quantitative gas/particle separation. Using this technique, hourly time resolution in-situ measurements of organic species were made and then used to investigate the pathways of gas-to-particle partitioning for oxygenated compounds and particle-phase organics were used for source apportionment calculations. The measurements of gas/particle partitioning of phthalic acid, pinonaldehyde and 6, 10, 14-trimethyl-2-pentadecanone were explored to elucidate the pathways of gas-to-particle partitioning whereby SOA was formed. The observations show that multiple pathways of gas-to-particle partitioning contribute to formation of SOA in the atmosphere and the dominance of different pathways are compound-dependent. Absorption into particles is shown to be the dominant pathway for 6, 10, 14-trimethyl-2-pentadecanone to contribute to SOA in Bakersfield, CA. The major pathway to form particle-phase phthalic acid is likely attributed to formation of condensable salts through reactions between phthalic acid and gas-phase ammonia. The observations of pinonaldehyde in particles while inorganic acids in particles were fully neutralized suggest that the occurrence of reactive uptake of pinonaldehyde onto particles does not require the presence of inorganic acids. The relationship between particle-phase pinonaldehyde and RH suggests that aerosol water content plays a significant role in the formation of particle-phase pinonaldehyde. To investigate the contributions of various sources to OA in Bakersfield, CA, positive matrix factorization (PMF) analysis was performed on a subset of the measured particle-phase organic compounds. Six OA source factors were identified, including one representing primary organic aerosol (POA), four different types of secondary organic aerosol (SOA) representing local, regional, and nighttime production, and one representing a complex mixture of additional OA sources that were not further resolvable. POA accounted for 15% of OA on average with a significant contribution from local vehicles. SOA was the dominant contributor to OA, accounting for on average 72% of OA. The rest of OA was unresolved as a mixture of OA sources. Both local and regional SOA had a significant contribution to OA during the day but regional SOA was the largest contributor to OA during the afternoon. SOA formed from the oxidation of biogenic SOA precursors substantially contributed to OA at night. The absorption of organic compounds into particles is suggested to be the major pathway to form SOA, although other pathways also played significant roles.

To achieve quantitative collection of SVOCs following improved gas/particle separation, a new collection and thermal desorption system was developed with the key component being a passivated metal fiber filter collector. This final configuration of the SV-TAG enabled in-situ quantitative measurements of speciated SVOCs with vapor pressures lower than n-tetradecane (C14). The capability for measurements of gas/particle partitioning was demonstrated by measurements of n-alkanes in both gas and particle phases. Organic tracers in both gas and particle phases can be quantified. Percentages of speciated organic compounds in total measured organics can be estimated. For example, ~7% and less than 1% of total measured organics in the same retention range of n-alkanes (C14-C20) in the atmosphere in Berkeley, CA were accounted for by the sum of measured n-alkanes (C14-C20) and the sum of n alkylcyclohexanes (C14-C20).

The SV-TAG has been demonstrated to enable investigation of the pathways of gas-to-particle partitioning and source apportionment of OA with hourly time resolution. The SV-TAG is also capable of quantitative measurements of speciated SVOCs, defining their gas/particle partitioning in-situ for the first time, and providing observational constraints on the abundance of SVOCs with which to investigate their primary emissions, chemical transformation, and fate.

Human activity significantly impacts the quantities, properties, and formationmechanisms of aerosols derived from biogenically produced organic chemicals. In this work, new methods are developed to expand speciated analysis of complex mixtures, and these methods are applied to two classes of human-impacted ambient aerosols: coastal marine aerosol, and tropical organic aerosol. The organic composition of both marine and tropical organic aerosol are largely uncharacterized, with over 85% of individual species separated and catalogued in each data set not present in current mass spectral libraries. Previously utilized methods for quantifying and characterizing novel atmospheric organics rely on manual judgements by individual researchers and are therefore highly inefficient and subject to errors that are difficult to quantify but assumed to be significant. To address this challenge, in Chapter 2 this work presents Ch3MS-RF, a machine learning-based model for predicting the chemical characteristics and instrument response factors of novel atmospheric organics based on their mass spectral fragmentation pattern and chromatographic retention. Chemical properties successfully modeled by Ch3MS-RF include carbon number, oxygen/carbon ratio, average carbon oxidation state, and volatility. This model achieves significant improvements in quantification accuracy over previous methods and enables novel atmospheric organics to be visualized in important chemical properties spaces for atmospheric chemistry, including the volatility basis set and Kroll diagram. Chapter 3 investigates the composition of the organic fraction of sea spray aerosol over a mesocosm phytoplankton bloom experiment conducted using coastal sea water. Results indicate that anthropogenic pollutants, including personal care products, oils, and urban compounds, significantly contribute to the organic fraction of sea spray aerosol, and that biological activity can transform this carbon pool by producing new biogenic species and transforming anthropogenic compounds. Chapter 4 focuses on a single class of anthropogenic coastal pollutants from the same experiment, the benzothiazoles. Benzothiazole is found to be emitted from ocean water in both gas and aerosol phases, and gas phase benzothiazole has the capacity to contribute to secondary aerosol formation when oxidized in the atmosphere. In the primary sea spray aerosol, a diverse suite of benzothiazole-containing species are observed, in concentrations and speciations that are not reflective of those observed in the dissolved organic phase in seawater. Chapter 5 applies similar methods to aerosol samples collected at a semiremote field site in the central Amazon which is impacted by both fires and urban emissions. A high degree of interseasonal uniqueness was observed in secondary products formed in the atmosphere, indicating significant seasonal dependencies of secondary aerosol formation processes. Unique products observed under pristine conditions in the Amazonian wet season and fire impacted conditions in the dry season are not currently included in mass spectral libraries and are not replicated using common laboratory oxidation techniques, highlighting the importance of expanding chamber oxidation studies to simulate a wider range of ambient conditions to elucidate important ambient reaction mechanisms. A chemically speciated view of how human activity alters the properties of terrestrial tropical and marine aerosols will improve our mechanistic understanding of anthropogenic effects on aerosol properties, thereby improving our ability to predict selected aspects of aerosol-climate feedbacks to changing human behavior.

Crude oil is an immensely complex mixture that contains thousands of distinct elemental compositions with hydrogen, carbon, oxygen, nitrogen, and sulfur atoms. The chemical fingerprint of a crude oil varies depending on its origin and degree of weathering, a phenomenon which includes biodegradation. This dissertation focuses on chemical composition of crude oil and its biodegradation with an emphasis on biosouring, an enzymatic process in which Sulfate Reducing microbial Communities (SRCs) reduce sulfate, thiosulfate, and elemental sulfur to sulfide. Biosouring in crude oil reservoirs results in hydrogen sulfide production, precipitation of metal sulfide complexes, increased industrial costs of petroleum production, and exposure issues for personnel. Potential treatment strategies for biosouring include the injection of nitrate or perchlorate anions into crude oil reservoirs. The objectives of this dissertation include development of new analytical techniques and their application to characterize the chemical composition of crude oil, and how it changes during biosouring and treatments, including substrate consumption and product formation.

Chapter 1 introduces the motivations for the research and analytical methods applied, including single and multi-dimensional gas chromatography with vacuum ultraviolet ionization and time-of-flight mass spectrometry (GC-VUV-TOF and GCxGC-VUV-TOF), gas chromatography combined with variable ionization time-of-flight-mass spectrometry (GC-Select-eV-TOF-MS), and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) combined with electrospray ionization. Chapter 1 then describes the experiments done examining biotransformations under different reducing environments and with different crude oils.

The ability to structurally characterize and isomerically quantify crude oil hydrocarbons relevant to refined fuels such as motor oil, diesel, and gasoline represents an extreme challenge for chromatographic and mass spectrometric techniques. In Chapter 2, GC×GC-VUV-TOF is applied using a tunable vacuum ultraviolet soft photoionization source, the Chemical Dynamics Beamline 9.0.2 of the Advanced Light Source at the Lawrence Berkeley National Laboratory, to directly characterize and isomerically sum the contributions of aromatic and aliphatic species to hydrocarbon classes of four crude oils. When the VUV beam is tuned to 10.5 ± 0.2 eV, both aromatic and aliphatic crude oil hydrocarbons are ionized to reveal the complete chemical abundance of C9–C30 hydrocarbons. When the VUV beam is tuned to 9.0 ± 0.2 eV only aromatic hydrocarbons are ionized, allowing separation of the aliphatic and aromatic fractions of the crude oil hydrocarbon chemical classes in an efficient manner while maintaining isomeric quantification. This technique provides an effective tool to determine the isomerically summed aromatic and aliphatic hydrocarbon compositions of crude oil, providing information that goes beyond typical GC×GC separations of the most dominant hydrocarbon isomers.

A comprehensive analysis of changes in crude oil chemical composition during biosouring and experimental treatments is presented in Chapter 3. Analyses using GC-VUV-TOF and FT-ICR MS combined with electrospray ionization were applied in this chapter to identify hydrocarbon degradation patterns and product formations in crude oil samples from biosoured, nitrate-treated, and perchlorate-treated bioreactor column experiments. Crude oil hydrocarbons were selectively transformed based on molecular weight and compound class in the biosouring control environment. Both the nitrate and the perchlorate treatments significantly reduced sulfide production; however, the nitrate treatment enhanced crude oil biotransformation, while the perchlorate treatment inhibited crude oil biotransformation. Nitrogen- and oxygen-containing biodegradation products, particularly with chemical formulas consistent with monocarboxylic and dicarboxylic acids containing 10−60 carbon atoms, were observed in the oil samples from both the souring control and the nitrate-treated columns but were not observed in the oil samples from the perchlorate-treated column. These results demonstrate that hydrocarbon degradation and product formation of crude oil can span hydrocarbon isomers and molecular weights up to C60 and double-bond equivalent classes ranging from straight-chain alkanes to polycyclic aromatic hydrocarbons. These results also strongly suggest that perchlorate injections may provide a preferred strategy to treat biosouring through inhibition of biotransformation.

Microbial catabolism is a natural biological process that can sour crude oil reservoirs, transform spilled oil, and is an engineering tool in hydrocarbon pollution remediation strategies. In Chapter 4, differences in hydrocarbon structure (such as degree of branching or position of alkyl substituents) are examined to determine how they affect relative catabolic degradation of alkanes, monocycloalkanes, and monoaromatic hydrocarbons in order to determine which compounds are altered most by these processes and which are recalcitrant. GC-Select-eV-TOF-MS at 14 eV was used to characterize catabolic patterns of hydrocarbon isomers in crude oil from four different oil fields exposed to a single complex microbial community. Changes in alkanes, monocycloalkanes, and monoaromatic hydrocarbons are comprehensively characterized to identify differences in biodegradation as a function of degree of branching and alkyl position. Hydrocarbon isomers with terminal alkyl branches were more prone to biodegradation than those with methyl groups further from the terminal position. Compounds with alkyl branches adjacent to each other experience less biodegradation than isomers with nonadjacent methyl groups. These patterns were consistent regardless of hydrocarbon structural class or oil composition, implying that isomeric structure, including the shape of the carbon chain and the alkyl position, dictates patterns of catabolism of hydrocarbons of a particular molecular class. The patterns identified in this chapter demonstrate that microbial metabolism leaves a distinct signature from other transformation processes occurring in spilled oil, such as atmospheric oxidation or evaporation, allowing the effects of biodegradation to be distinguished from those of other processes acting upon weathered oil.

A summary of research implications and ideas for further research directions, including incorporation of isotope labeled tracers to track a compound’s specific biodegradation pathway and characterization of volatile organic compounds (VOCs) from biodegrading microbial communities, are provided in Chapter 5.

Particles in the atmosphere are known to have negative health effects and important but highly uncertain impacts on global and regional climate. A majority of this particulate matter is formed through atmospheric oxidation of naturally and anthropogenically emitted gases to yield highly oxygenated secondary organic aerosol (SOA), an amalgamation of thousands of individual chemical compounds. However, comprehensive analysis of SOA composition has been stymied by its complexity and lack of available measurement techniques. In this work, novel instrumentation, analysis methods, and conceptual frameworks are introduced for chemically characterizing atmospherically relevant mixtures and ambient aerosols, providing a fundamentally new level of detailed knowledge on their structures, chemical properties, and identification of their components. This chemical information is used to gain insights into the formation, transformation and oxidation of organic aerosols.

Biogenic and anthropogenic mixtures are observed in this work to yield incredible complexity upon oxidation, producing over 100 separable compounds from a single precursor. As a first step toward unraveling this complexity, a method was developed for measuring the polarity and volatility of individual compounds in a complex mixture using two-dimensional gas chromatography, which is demonstrated in Chapter 2 for describing the oxidation of SOA formed from a biogenic compound (longifolene: C15H24). Several major products and tens of substantial minor products were produced, but none could be identified by traditional methods or have ever been isolated and studied in the laboratory. A major realization of this work was that soft ionization mass spectrometry could be used to identify the molecular mass and formula of these unidentified compounds, a major step toward a comprehensive description of complex mixtures. This was achieved by coupling gas chromatography to high resolution time-of-flight mass spectrometry with vacuum ultraviolet (VUV) photo-ionization. Chapters 3 and 4 describe this new analytical technique and its initial application to determine the structures of unknown compounds and formerly unresolvable mixtures, including a complete description of the chemical composition of two common petroleum products related to anthropogenic emissions: diesel fuel and motor oil. The distribution of hydrocarbon isomers in these mixtures - found to be mostly of branched, cyclic, and saturated - is described with unprecedented detail.

Instead of measuring average bulk aerosol properties, the methods developed and applied in this work directly measure the polarity, volatility, and structure of individual components to allow a mechanistic understanding of oxidation processes. Novel characterizations of these complex mixtures are used to elucidate the role of structure and functionality in particle-phase oxidation, including in Chapter 4 the first measurements of relative reaction rates in a complex hydrocarbon particle. Molecular structure is observed to influence particle-phase oxidation in unexpected and important ways, with cyclization decreasing reaction rates by ~30% and branching increasing reaction rates by ~20-50%. The observed structural dependence is proposed to result in compositional changes in anthropogenic organic aerosol downwind of urban areas, which has been confirmed in subsequent work by applying the techniques described here.

Measurement of organic aerosol components is extended to ambient environments through the development of instrumentation with the unprecedented capability to measure hourly concentrations and gas/particle partitioning of individual highly oxygenated organic compounds in the atmosphere. Chapters 5 and 6 describe development of new procedures and hardware for the calibration and analysis of oxygenates using the Semi-Volatile Thermal desorption Aerosol Gas chromatograph (SV-TAG), a custom instrument for in situ quantification of gas- and particle-phase organic compounds in the atmosphere. High time resolution measurement of oxygenated compounds is achieved through a reproducible and quantitative methodology for in situ "derivatization" - replacing highly polar functional groups that cannot be analyzed by traditional gas chromatography with less polar groups. Implementation of a two-channel sampling system for the simultaneous collection of particle-phase and total gas-plus-particle phase samples allows for the first direct measurements of gas/particle partitioning in the atmosphere, significantly advancing the study of atmospheric composition and variability, as well as the processes governing condensation and re-volatilization.

This work presents the first in situ measurements of a large suite of highly oxygenated biogenic oxidation products in both the gas- and particle-phase. Isoprene, the most ubiquitous biogenic emission, oxidizes to form 2-methyltetrols and C5 alkene triols, while α-pinene, the most common monoterpene, forms pinic, pinonic, hydroxyglutaric, and other acids. These compounds are reported in Chapter 7 with unprecedented time resolution and are shown for the first time to have a large gas-phase component, contrary to typical assumptions. Hourly comparisons of these products with anthropogenic aerosol components elucidate the interaction of human and natural emissions at two rural sites: the southeastern, U.S. and Amazonia, Brazil. Anthropogenic influence on SOA formation is proposed to occur through the increase in liquid water caused by anthropogenic sulfate. Furthermore, these unparalleled observations of gas/particle partitioning of biogenic oxidation products demonstrate that partitioning of oxygenates is unexpectedly independent of volatility: many volatile, highly oxygenated compounds have a large particle-phase component that is poorly described by traditional models. These novel conclusions are reached in part by applying the new frameworks developed in previous chapters to understand the properties of unidentified compounds, demonstrating the importance of detailed characterization of atmospheric organic mixtures.

Comprehensive analysis of anthropogenic and biogenic emissions and oxidation product mixtures is coupled in this work with high time-resolution measurement of individual organic components to yield significant insights into the transformations of organic aerosols. Oxidation chemistry is observed in both laboratory and field settings to depend on molecular properties, volatility, and atmospheric composition. However, this work demonstrates that these complex processes can be understood through the quantification of individual known and unidentified compounds, combined with their classification into descriptive frameworks.

Modern human populations spend ~90% of their time indoors. Moreover, concentrations of well-studied organic chemicals in indoor air are often orders of magnitude higher than equivalent outdoor concentrations. Considering that airborne organic pollutants can impact human and environmental health, it is critical to understand the sources, physicochemical behavior and modes of exposure of airborne organic chemicals in the indoor environment. This dissertation improves scientific understanding of these topics via analysis of time-resolved measurements of organic pollutants acquired in three normally-occupied residences and test houses over several months.

Until recently, researchers have largely used offline measurement approaches to study indoor air quality. Time-averaged samples are collected over a period spanning hours to weeks and then returned to the laboratory for subsequent analysis. While this approach is well-suited for survey-based analyses where pollutant concentrations are measured at many different sampling sites, the limited time-resolution inhibits study of dynamic processes that influence indoor air quality. Recent advances in instrumentation permit continuous monitoring of airborne organic chemicals with high chemical specificity on minute-by-minute and hourly time-scales over extended observation periods. This dissertation reports key findings from several months of time-resolved measurements of volatile organic compounds (VOCs) as measured by proton-transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) and semivolatile organic compounds (SVOCs) as measured by semivolatile thermal desorption aerosol gas chromatography in two normally-occupied residences (H1, H2) and a test house with scripted experiments (HOMEChem).

In Chapter 2, time-varying concentrations and gas-particle phase partitioning of phthalate diesters, a class of compounds of public-health interest, are reported at the H2 site. The dynamic behavior of four reported phthalates is observed to be related to their vapor pressure and physicochemical parameters such as temperature and particle mass concentration. These findings are generalized in Chapter 3 where it is suggested that volatility-dependent partitioning processes are the principle drivers of SVOC dynamic behavior. As part of this analysis, observations are connected to a theoretical model that assumes kinetic equilibrium with organic surface films commonly found indoors. Furthermore, it is observed that certain SVOCs can be deposited on surfaces during large emission events and then re-emitted into bulk air during future particle-emission events. In these scenarios, particles were inferred to enhance mass transport from condensed-phase reservoirs to bulk air. A high-resolution exposure assessment is conducted for VOCs in Chapters 4 and 5. Source apportionment analysis, a risk-based prioritization analyses and experimental estimates of intake fractions are reported for >200 VOCs. In contrast to expectations, a key finding suggests that for most VOCs, time-averaged exposure are attributable to the building and its static contents rather than episodic emission-events like cooking related to occupants or outdoor-to-indoor transport.