The Effect of Organics on Particle Formation and Growth from Methanesulfonic Acid, Amines and Water

Atmospheric particles negatively affect human health, limit visibility and impact climate. Their deleterious effects are known, but the mechanism of how particles form and grow in the atmosphere is not fully understood. Sulfuric acid (H2SO4) is a large contributor to particle formation, but nucleation of H2SO4-H2O cannot explain atmospheric observations. Ammonia (NH3) can form particles with sulfuric acid, yet the ternary nucleation of H2SO4-NH3-H2O still does not match measurements, indicating the participation of other precursors. Amines have been shown to enhance particle formation and, despite their lower concentrations in air, can displace NH3 in clusters. As the use of sulfur-based fossil fuels is phased out, and consequently H2SO4 concentrations are reduced, methanesulfonic acid (MSA) is expected to become a more important source of particles. MSA does not form particles efficiently with water alone, but does so with amines and water. The reaction of MSA and ammonia/amines is dependent on relative humidity, basicity and amine structure. In this dissertation, the effect of four organic compounds on the reaction of methanesulfonic acid, amines and water is investigated. Experiments are conducted in a small volume aerosol flow reactor at ambient temperature and atmospheric pressure (294 K, 1 atm). Early experiments show that the aerosol flow reactor is sensitive to order of addition of reactants. Laboratory results are interpreted along with results of theoretical calculations of initial clusters completed by the Gerber group. Results show that particle formation is influenced by proton transfer, hydrogen bonding capacity and basicity. Molecular structure can also impact particle formation and growth by influencing how initial clusters grow to detectable particles. Particle formation from organics and amines with and without water is inefficient in this system. Results show that, in the atmosphere, water likely overwhelms the effect of organics. Theoretical calculations give insight on how experimentally unobservable initial clusters of these systems correlates with detectable particles. The results of this work could aid atmospheric models in more accurately predicting the impact of particles on a regional and global level