Application of atmospheric chemistry has been the cornerstone of California’s landmark air quality improvement over the 20th century. Yet challenges with pesticides, poor air quality, and disproportionate pollution burdens in environmental justice communities continue to evolve in the 21st century. The majority of this work developed techniques to characterize the atmospheric fates of neonicotinoid pesticides, which are now the world’s most commonly used insecticides. Laboratory studies were conducted to evaluate the heterogeneous photochemistry and OH radical oxidative reactions with selected neonicotinoid pesticides, as well as potential matrix effects due to commercial formulations and application type. Estimated atmospheric lifetimes are reported and the reaction products are identified.

A second project, completed in collaboration with the California Air Resources Board and in partial fulfillment of the Ridge to Reef professional development traineeship, evaluated the impact of increasing wildfires on ozone formation and NAAQS attainment across three air basins in California, the San Joaquin Valley, the South Coast Air Basin, and the Sacramento Valley. Results demonstrated the need for simultaneous NOx and VOC reductions across the air basins to meet ozone attainment requirements, with implications for prescribed burning techniques to reduce ozone and PM2.5 pollution.

Atmospheric particles adversely affect climate, visibility, and health and thus the need to understand their formation and growth mechanisms is essential. However, the lack of complete understanding of these mechanisms may be a result of the complexity of the interactions between gas and particle phase species. Model systems of atmospherically relevant species are often utilized to better understand the chemistry of these reactions in the atmosphere.

This dissertation work explores uptake and reaction of various atmospherically relevant reaction systems to determine if the chemical properties of the gas and condensed phases affect the mechanism of uptake. In the first approach, attenuated total reflectance–Fourier transform infrared (ATR–FTIR) spectroscopy was used to measure the uptake of various gas phase species on different low viscosity liquids and on secondary organic aerosol (SOA) generated from the ozonolysis of α–pinene. Uptake of gas phase isobutyl nitrate (IBN) into squalane and Fomblin ® was rapid, with equilibrium established quickly. A higher concentration of gas phase IBN was needed to see uptake into Fomblin ®, which may be due to the increased number of polar groups compared to squalane. Uptake of IBN onto laboratory generated SOA was much slower than squalane, which may be indicative of the much higher viscosity of SOA. Polar compounds were readily taken up onto the clean ATR crystal, even with a self–assembled monolayer fixed to the crystal surface.

The second system of interest was the reaction between gas phase amines and solid dicarboxylic acids (diacids), which was carried out using two different techniques. The first technique utilized a flow reactor coupled to a quadrupole mass spectrometer. The second method involved a Knudsen cell interfaced to the mass spectrometer. Uptake coefficients for n–butylamine on solid C2 – C5 diacids were on the order of 10-3 – 10-2 using the flow reactor. Experiments conducted using the Knudsen cell had measured uptake coefficients from 10-1 to ≤ 10-6, depending on the number of carbon atoms in the diacid chain. Those experiments performed using the flow reactor were operated at time constants that may have been too slow to capture the initial uptake of the amine onto the diacid. This manifest itself into a lack of difference in uptake coefficients between diacids, as well as signs of surface saturation. Further exploration of this reaction using the Knudsen cell concluded that uptake coefficients for odd carbon number diacids are orders of magnitude larger than the even carbon number diacids. This difference is due to the dissimilarities in packing of the crystal structures, as well as the formation of an ionic liquid layer on the surface that is able to provide replenishment of the diacid. Subsequent studies of different primary amines, as well as dimethylamine, trimethylamine, and ammonia show that structure of the amine also affects the kinetics and formation of the ionic liquid layer.

These reaction systems show that the nature of the gas and condensed phase species both play a large role in uptake and reaction of the gas phase. Results from these experiments show that overall assumptions in the interactions between the gas and condensed phases may not be accurate in predicting concentrations of atmospheric particles. Experiments carried out on these reaction systems highlight the benefits of studying model systems in order to gain a better understanding of one component of atmospheric interactions between two species. Ultimately, these and other model systems will help build a better understanding on a molecular level of the chemistry behind particle growth in the atmosphere.

Atmospheric aerosols reduce visibility, adversely affect human health, and influence the climate. However, modeling the evolution of these systems is complicated by the large number of species involved and their complex interactions in both the gas and particle phase. To reduce this complexity, key species and generalized mechanisms of particle formation, growth and evolution are sought to aid development of computationally-feasible regional and global atmospheric models. These models, alongside simple, accurate measurement techniques for particles and key gas-phase precursors, will improve predictions of the effects of changing emissions on visibility, climate and human health.

This dissertation reports work identifying a new source of particles in the atmosphere, those formed from methanesulfonic acid (MSA), amines and water. Experiments performed in an aerosol flow reactor with MSA, water vapor, and dimethylamine or trimethylamine demonstrate that this system rapidly forms particles, and that all three species (MSA, water and amine) are required for significant particle formation. A simplified kinetics mechanism for particle formation from this system was developed based on these experiments and theoretical calculations of small clusters of these species, performed by the Gerber group. Predictions of particle formation from this mechanism agree well with our measurements, making this computationally inexpensive calculation useful for large-scale atmospheric models. A more comprehensive aerosol model is under development to test this mechanism while incorporating the effects of wall losses, coagulation between particles, and growth based on particle-phase activity.

Predicting particle formation in the laboratory and the real atmosphere requires accurate measurement techniques for the gas-phase precursors. A major limitation to many existing techniques for measuring gas-phase amines is rapid loss of the analyte to instrument surfaces, such as inlet tubing. A new technique for measuring gas-phase ammonia and amines was developed that involves collection of the sample on weak ion-exchange resin in a cartridge designed to minimize the exposure of the incoming sample to surfaces prior to uptake on the resin. These cartridges are simultaneously extracted and analyzed by ion chromatography, using a novel instrument configuration designed to lower the detection limit of this method to the parts-per-trillion level in air for a 60 min sample. This technique using inexpensive, reusable cartridges is shown to efficiently measure ammonia and three aliphatic amines.

Unlike MSA, ammonia and amines have high vapor pressures and must be neutralized to remain in the particle phase. This opens the possibility of complex displacement reactions between gas- and particle-phase ammonia and amine species. Experiments were performed in collaboration with scientists at PNNL's EMSL User Facility using the SPLAT-II single-particle mass spectrometer to investigate the displacement of ammonia and amines in ammonium- and aminium-methanesulfonate particles on addition of a different gas-phase amine. The results suggest a complex system where the effects of particle-phase ammonium or aminium on hygroscopicity and particle phase result in different degrees of displacement by gas-phase amines.

The work presented here will aid in the development and evaluation of regional and global atmospheric models, by identifying and quantifying new sources of particles, understanding complex reactions affecting particle growth, and facilitating simple, accurate measurements of gas-phase particle precursors in the field.