Atmospheric aerosols deteriorate visibility and pose a significant risk to human health. The global fluxes of secondary organic aerosols (SOA) that form in the atmosphere from aromatic hydrocarbons are poorly constrained and highly uncertain. The lack of molecular tracers to quantify anthropogenic SOA (ASOA) in part limits the understanding of its abundance and variability, and results in a systematic underestimation of the role of ASOA in the atmosphere. The research presented in this thesis advances the knowledge about ASOA through the i) development of new and advanced methods to quantify potential ASOA tracers, ii) evaluation of their suitability as tracers for ASOA, and iii) application of the validated tracers to assess the spatial, diurnal and seasonal variation of ASOA in three urban environments. In this research, a greater understanding of the role of ASOA is gained through the expansion of tracers for SOA from aromatic hydrocarbons. An analytical method to quantify furandiones, which are produced in high yields from the photooxidation of aromatic hydrocarbons, was developed and enabled the first ambient measurements of furandiones. The optimized method allows for the simultaneous extraction of primary source tracers (e.g., polycyclic aromatic hydrocarbons, hopanes, levoglucosan) and other potential ASOA tracers (e.g., 2,3-dihydroxy-4-oxopentanoic acid [DHOPA], benzene dicarboxylic acids, and nitromonoaromatics). The systematic evaluation of potential ASOA tracers by their detectability, gas-particle partitioning, and specificity revealed that DHOPA, phthalic acid, 4-methylphthalic acids, and some nitromonoaromatics are good ASOA tracers because they are specific to aromatic hydrocarbon photooxidation, readily detected in ambient air, and substantially partition to the particle phase under ambient conditions. These tracers are thus recommended for use in field studies to estimate ASOA contributions to atmospheric aerosol relative to other sources. ASOA was determined to be a significant contributor to PM2.5 organic carbon (OC) in three urban environments. In the industrial Houston Ship Channel area in Houston, TX, ASOA contributed 28% of OC, while biogenic SOA (BSOA) contributed 11%. Diurnally, ASOA peaked during daytime and was largely associated with motor vehicle emissions. In Shenzhen, a megacity in China, 13-23% of OC mass was attributed to ASOA, three folds higher than BSOA. When China controlled the emissions from fossil fuel-related sources, the ASOA contribution to OC reduced by 42-75% and visibility remarkably improved. In downtown Atlanta, GA, ASOA contributed 29% and 16% of OC during summer and winter, respectively. ASOA dominates over BSOA during winter, while high biogenic VOC fluxes made BSOA the major SOA source in Atlanta, GA during summertime. These results indicate the high abundance of ASOA in urban air that has potential to be reduced by modification of anthropogenic activities. Overall, the work presented in this dissertation advances the knowledge about the abundance and variation of ASOA in urban atmospheres through the development of quantification methods and expansion of ASOA tracers. These tracers improve source apportionment of ASOA in receptor based models, which can ultimately aid in developing and implementing effective strategies for air quality management.

Direct reading instruments (DRIs) are popular devices for measuring aerosols because they provide rapid on-site measurement of particle size and/or concentration. However, the output of DRIs may drift over time requiring frequent manufacturer calibration. Given the possibility of drift, the output of DRIs should ideally be verified to ensure proper response before and after field use. Methods for verifying the output of DRIs particle size reading are available for use in laboratory and field. However, methods for verifying the DRIs concentration reading are complex and often use of stationary installations that are not suited for field work. The objective of this study was to develop a verification device that can be used in the field to verify the output of DRIs for measuring aerosol concentration. The new device uses a nebulizer that produces aerosols through vibrating mesh technology. This vibrating mesh nebulizer (VMN) uses only electrical input to generate aerosols and does not require compressed air. The verification device was able to produce stable output of aerosols at low concentrations (0.2 mg/m3 to 1.2 mg/m3). It was also possible to produce different concentration levels of aerosol by changing the electrical current to the VMN. The verification device was used to monitor and validate the output of a condensation particle counter and a photometer. Results showed that both instruments having valid output and did not require manufacture calibration. The verification device made it possible to monitor and verify the output of two DRIs. This was achieved by generating reproducible aerosol output with specific composition. This verification device presents a practical method to verify the concentration output of DRIs for measuring aerosols.

The Aglite system is a three-wavelength lidar plus a suite of instruments for measuring particulate emission levels near agricultural facilities. The lidar performs 3D scans of the air surrounding the facility and maps the concentration of particulates in the atmosphere surrounding the facility with high spatial and temporal resolution. Data from the conventional instruments are used to calibrate the lidar. The Aglite system includes a retrieval program, which combines the data from the lidar instrument with data from the conventional instruments to produce measurements of particulate concentration values. This thesis describes the design of the lidar data retrieval program, the development and implementation of the algorithm, and the results of measurements made on the initial field campaign. The methodology used by the Aglite system, the details of the retrieval algorithm, and the results of the measurements made by the instrument on its first field campaign are described.

acase@tulane.edu

A Dylos DC1100 was evaluated to: 1. Establish relationship between low-cost DC1100 and higher-cost pDR 1200; 2. Develop a method to convert DC1100 particle number into mass concentration to compare with respirable and inhalable mass references. A Dylos DC1100 was deployed in a swine CAFO, along with a pDR-1200 and filter set to collect respirable and inhalable particles. Deployment was conducted from December 2013 through February 2014 in 24 hour intervals. The pDR-1200 and respirable mass concentration was used to convert the DC1100 particle count to mass concentration. Two methods of conversion were used, physical property method (Method 1) and regression method (Method 2). Direct measurements from the DC1100 and pDR-1200 had a coefficient of determination (R2) of 0.85. DC1100 particle number were converted to mass concentration using Method 1 and Method 2, the coefficient of determination (R2) was 0.72 and 0.73, respectively compared to pDR-1200. The slope of the best-fit line was 1.01 for Method 1 and 0.70 for Method 2. When the DC1100 daily averages were compared to respirable mass, the physical property method had an R2 of 0.64 and a slope of 1.10. Regression method had an R2 of 0.62 and a slope of 0.80. Both methods underestimated inhalable mass concentrations with slopes < 0.13. The Dylos DC1100 can be used to estimate respirable mass concentrations within a CAFO. Using expensive dust monitors to correct the number of particles into a mass concentration is needed to establish a correction factor for the DC1100. Using these methods, correction factors can be determine for many occupational environment, with the physical property method being preferred over the regression method.

The contribution of atmospheric aerosols towards radiative forcing has a very high uncertainty due to their short atmospheric lifetime. The aerosol effects are largely controlled by the density, elemental composition, and hygroscopic properties of the aerosol particles. Therefore, we have performed designed new methodology using Scanning Transmission X-ray Microscopy (STXM), Atomic force spectroscopy (AFM), micro-FTIR spectroscopy and Scanning Electron Microscopy (SEM) to quantify these important aerosol properties. Hygroscopic properties are quantified by plotting the mass of water on a single particle basis, calculated from STXM, as a function of relative humidity. Alternatively, micro-FTIR spectra have been used to study the effect of composition of aerosol particles on the hygroscopic properties of NaCl. Moreover, a unique combination of STXM and AFM has been utilized to quantify density and elemental composition of micrometer dimensional particles. This method has also been extended towards exploring mixing state of particles, consisting of heterogeneously mixed inorganic and organic compounds. In addition to these above mentioned properties, the fate of an atmospheric particle is often altered by chemical transformation and that in turn is influenced by the atmospheric RH. Therefore, we have studied an unusual keto-enol tautomerism in malonic acid particles at high RH, which is not observed in bulk. This observation could potentially be utilized to significantly improve the models to estimate Secondary Organic Aerosols (SOA). Using STXM and micro-FTIR technique, RH dependent equilibrium constant of the tautomerism reaction has been quantified as well. Organic nanocrystals capable of undergoing solid state photochemical changes in a single-crystal-to-single-crystal (SCSC) manner have been particularly important in fabricating molecular switches, data storage devices etc. Mechanical properties of these nanomaterials may control its SCSC reactivity. In addition, investigation of mechanical stiffness is important to define allowable limit of stiffness towards device application. Therefore, we studied mechanical properties of series organic nano cocrystals primarily consisting of trans-1,2-bis(4-pyridyl)ethylene and substituted resorcinol using AFM nanoindentation technique. Dependence of mechanical properties and SCSC reactivity on the resorcinol structure is also investigated as well. Moreover, photolithography on the thin film of these organic cocrystals has been performed to demonstrate its applicability as a photoresist.

Particulate matter (PM) suspended in air varies in size from nanometers to micrometers and contains a wide range of chemical components, including organic compounds, black carbon (soot), inorganic minerals and metals. Atmospheric aerosols are generated from either primary sources like volcanic eruptions, re-suspended soil dust, sea spray, vegetative detritus, fossil fuel and biomass combustion emissions; or secondary atmospheric reactions via gas-to-particle conversion of atmospheric gases. Particle size, abundance, and chemical composition determine how a particle interacts with light and other atmospheric constituents (e.g. gases, water vapor) in addition to its impact on human health. While atmospheric scientists have been working on characterizing atmospheric aerosols for many years, major gaps persist in understanding the properties of many globally-important sources. This dissertation provides new understanding of the chemical composition of biomass burning and sea spray aerosols. PM emissions from biomass burning vary by fuel, and depend on fuel type and composition, moisture content, and combustion conditions. Although biomass smoke is critically important in global climate and local-regional health impacts, the physical and chemical composition of biomass burning aerosol is still not fully understood in the case of peat, agricultural residues and cooking fires. The Fire Laboratory at Missoula Experiments (FLAME) were designed to fulfill these gaps to improve our understanding in both historically undersampled and well-studied fuels while adding new instrumentation and experimental methods to provide previously unavailable information on chemical properties of biomass burning emissions. Globally-important biomass fuels were combusted in a controlled environment, and PM was chemically characterized to compute fuel based emission factors (EF) as the amount of chemical species released per unit mass of fuel burned. We showed that chemical composition of PM varies for different fuel types and certain fuels types (e.g., peat and ocote) emit considerably high concentrations of polycyclic aromatic compounds that are associated with negative health effects. We also showed that PM from biomass smoke contains fluoride for the first time, at approximately 0.1% by weight. With respect to the annual global emissions of PM due to biomass burning, this makes biomass burning an important source of fluoride to the atmosphere. Further, peatland fire emissions are one of the most understudied atmospheric aerosol sources but are a major source of greenhouse gases globally and cause severe air quality problems in Asia. This thesis provides the first field-based emissions characterization study, for samples collected at peat burning sites in Central Kalimantan, Indonesia. Using these EFs and estimates of the mass of fuel burned, it was estimated that 3.2 - 11 Tg of PM2.5 were emitted to atmosphere during 2015 El Niño peat fire episode which is ~10 % of estimated total annual PM flux for biomass burning. Overall, these studies computed more representative EFs for previously undersampled sources like peat, and previously unidentified chemical species like fluoride that can be used to update regional and global emission inventories. The concentration and composition of organic compounds in sea spray aerosol (SSA) alters its optical properties, hygroscopicity, cloud condensation, and ice nucleation properties and thus affects Earth’s radiative budget. In the past, SSA has been difficult to characterize, because of low concentrations relative to background pollutants. Nascent SSA was generated during a mesocosm, using a wave-flume at the University of California, San Diego and was characterized for saccharides and inorganic ions in order to assess their relative enrichment in fine (PM2.5) and coarse (PM10-2.5) SSA and sea surface microlayer (SSML) relative to seawater. For the first time, we showed that saccharides comprise a significant fraction of organic matter in fine and coarse SSA contributing 11 % and 27 %, respectively. Relative to sodium, saccharides were enriched 14-1314 times in fine SSA, 3-138 times in coarse SSA, but only up to 1.0-16.2 times in SSML. The saccharide and ion concentration in SSML and persistent whitecap foam was quantitatively assessed by another mesocosm study performed under controlled conditions. We demonstrated that relative to sodium, saccharides were enriched 1.7-6.4 times in SSML and 2.1-12 times in foam. Higher enrichment of saccharides in foam over the SSML indicates that surface active organic compounds become increasingly enriched on aged bubble film surfaces. Similarly, we showed that fine SSA contains saccharides characteristic of energy-related polysaccharides, while coarse SSA contains saccharides that are characteristic of structure-related polysaccharides. The ultrafiltration studies showed that structure-related polysaccharides effectively coagulate to form large particulate organic matter and size is likely the reason for their exclusion from small SSA. The enrichment of organic species in SSML, foam and SSA led to an enrichment of inorganic ions probably through chelation with organic molecules. Mean enrichment factors for major ions demonstrated the highest enrichment in fine SSA for potassium (1.3), magnesium (1.4), and calcium (1.7). Consequently, due to these organic and inorganic enrichments, SSA develops a significantly different chemical profile compared to seawater. These improved chemical profiles of SSA should be used to develop laboratory proxies to further study the transfer of organic matter across the ocean-air interface and the physical properties of SSA. . Overall, the results presented in this dissertation provide new chemical profiles for previously understudied emission sources like peatland fire emissions, and previously unquantified chemical species like F- in biomass burning emissions and enrichment of saccharides and ions in SSA. These data could be used in updating regional and global emission inventories, atmospheric modeling and human exposure studies.

Traditional aerosol samplers are limited in their abilities to collect large quantities of particulate matter due to their low flow rates, high pressure drops, and are noise intrusiveness. The goal of this study was to develop an alternate aerosol sampler using electrostatic precipitation technology that was safe and not noise intrusive to be deployed in homes. The O-Ion B-1000 was selected as the most suitable electrostatic precipitator (ESP) for achieving the goal of this study because of its affordability, the design of its collection electrode and its high flow rate. The collection efficiency of the ESP was assessed for three aerosols; Arizona Road Dust (ARD), NaCl and diesel fumes. ARD was found to have the highest average collection efficiency (65%) followed by NaCl (43%) and lastly diesel fumes (41%). A method for recovering the particulate matter deposited on the collection electrode was developed. The dust collected on the electrode was recovered onto polyvinyl chloride (PVC) filters moistened with deionized water. Additionally, the recovery of the three test aerosols, ARD, NaCl, and diesel fumes, from the collection electrode was assessed. A gravimetric analysis was done to determine the amount of dust recovered. The collection efficiency was used to calculate the amount of mass expected on the filter for a particular aerosol. NaCl had the highest recovery at 95% recovery, followed by ARD (73%) and lastly diesel fumes (50%). Two identical ESPs were also deployed in an office and in a bedroom, 104.47 mg and 9.64 mg of particulate matter (PM) was recovered respectively. The noise and ozone level produced by the ESP was evaluated to determine the ESP’s viability as a household aerosol sampler. The ESP’s high setting had a noise level of 45.8 dB and ozone generation rate of 0.036 mg/min. The results of the calculation showed that in an averaged size unventilated room (6.10 m × 6.10 m × 2.44 m), it would take 6 hours and 53 minutes for the ozone levels to reach the recommended maximum exposure limits per National Ambient Air Quality Standards (NAAQS). Additionally, a ventilation of 230 L/min is needed in order to prevent the ozone levels generated by the ESP from exceeding maximum exposure limits per NAAQS. Overall, the O-Ion B-1000 met the criteria of collecting 1 mg of PM in a 24 hour sampling for ARD and NaCl. Diesel fumes however, required 30 hours to collect 1 mg of PM. The noise levels generated by the ESP set on high was one dB above the Environmental Protection Agency (EPA) standards for indoor noise limit. However, the noise is proportional to inverse distance squared; the ESP should not pose a problem during household deployment. Ozone generated by the ESP was also found to be below 0.07 ppm as set by the EPA with an average ventilation of 230 L/min. The average ventilation of a household is 1500 L/min, thus the ozone generated by the ESP would not surpass 0.07 ppm. However, the ESP should not be deployed in unventilated rooms for a period of more than 6 hours and 53 minutes.

Currently, there exists a great deal of uncertainty regarding atmospheric aerosols and the role that they play within the Earth’s atmosphere. It is known that atmospheric aerosols can play a role in the Earth’s climate by scattering and absorbing solar radiation or acting as a cloud condensation nuclei. The purpose of this work is to obtain an improved understanding of the chemistry of atmospheric aerosols to better determine their impacts the environment, air quality, and climate. This work revolves around one specific type of atmospheric aerosol, i.e. sea spray aerosol. Sea spray aerosol is generated via breaking waves, through wind-driven mechanisms. Ocean water covers roughly 71% of the Earth’s surface, and from this over 1300 Tg of sea spray aerosols is emitted into the atmosphere every year. However, until recently, the study of sea spray was very challenging and often inconclusive due to the inability to filter background particles out. In this work, the understanding of sea spray aerosol is progressed by taking a two-pronged approach. First, this work focuses on the study of model systems of simple ocean surfactants and NaCl and the change in chemistry that occurs when the two are in the presence of each other. Second, sea spray samples generated during a biological bloom are isolated and analyzed. Using this two pronged approach, it is shown that model systems can provide supporting evidence for hypotheses created from trends discovered in more complex samples. Finally, common aerosol generation, storage, and analysis techniques are studied in order to improve our understanding of their effects on aerosol particles.

The purpose of this research is to demonstrate the ability to generate and characterize a nanometer sized aerosol using solutions, suspensions, and a bulk nanopowder, and to research the viability of using an acoustic dry aerosol generator/elutriator (ADAGE) to aerosolize a bulk nanopowder into a nanometer sized aerosol. The research compares the results from a portable scanning mobility particle sizer (SMPS) to the more traditional method of counting and sizing particles on a filter sample using scanning electron microscopy (SEM). Sodium chloride aerosol was used for the comparisons. The sputter coating thickness, a conductive coating necessary for SEM, was measured on different sizes of polystyrene latex spheres (PSLS). Aluminum oxide powder was aerosolized using an ADAGE and several different support membranes and sound frequency combinations were explored. A portable SMPS was used to determine the size distributions of the generated aerosols. Polycarbonate membrane (PCM) filter samples were collected for subsequent SEM analysis. The particle size distributions were determined from photographs of the membrane filters. SMPS data and membrane samples were collected simultaneously. The sputter coating thicknesses on four different sizes of PSLS, range 57 nanometers (nm) to 220 nm, were measured using transmission electron microscopy and the results from the SEM and SMPS were compared after accounting for the sputter coating thickness. Aluminum oxide nanopowder (20 nm) was aerosolized using a modified ADAGE technique. Four different support membranes and four different sound frequencies were tested with the ADAGE. The aerosol was collected onto PCM filters and the samples were examined using SEM. The results indicate that the SMPS and SEM distributions were log-normally distributed with a median diameter of approximately 42 nm and 55 nm, respectively, and geometric standard deviations (GSD) of approximately 1.6 and 1.7, respectively. The two methods yielded similar distributional trends with a difference in median diameters of approximately 11 - 15 nm. The sputter coating thickness on the different sizes of PSLSs ranged from 15.4 - 17.4 nm. The aerosols generated, using the modified ADAGE, were low in concentration. The particles remained as agglomerates and varied widely in size. An aluminum foil support membrane coupled with a high sound frequency generated the smallest agglomerates. A well characterized sodium chloride aerosol was generated and was reproducible. The distributions determined using SEM were slightly larger than those obtained from SMPS, however, the distributions had relatively the same shape as reflected in their GSDs. This suggests that a portable SMPS is a suitable method for characterizing a nanoaerosol. The sizing techniques could be compared after correcting for the effects of the sputter coating necessary for SEM examination. It was determined that the sputter coating thickness on nano-sized particles and particles up to approximately 220 nm can be expected to be the same and that the sputter coating can add considerably to the size of a nanoparticle. This has important implications for worker health where nanoaerosol exposure is a concern. The sputter coating must be considered when SEM is used to describe a nanoaerosol exposure. The performance of the modified ADAGE was less than expected. The low aerosol output from the ADAGE prevented a more detailed analysis and was limited to only a qualitative comparison. Some combinations of support membranes and sound frequencies performed better than others, particularly conductive support membranes and high sound frequencies. In conclusion, a portable SMPS yielded results similar to those obtained by SEM. The sputter coating was the same thickness on the PSLSs studied. The sputter coating thickness must be considered when characterizing nanoparticles using SEM. Finally, a conductive support membrane and higher frequencies appeared to generate the smallest agglomerates using the ADAGE technique.