UC Irvine

The composition and physical properties of atmospheric particles play a critical in Earth’s radiativebalance and are major sources of uncertainty in understanding our global climate. Atmospheric particles are produced through a variety of processes and their atmospheric impacts depend on multiple factors, like the composition, size and number concentration. Particularly, the composition, formation and growth of ultrafine particles, defined as particles with a diameter less than 100 nm, are of particular interest to investigate due to their ability to directly serve as cloud condensation nuclei (CCN). However, these various chemical and physical properties of ultrafine particles are largely dependent upon the environment they originate from. Therefore, studying the composition of ultrafine particles across various locales is extremely important and these results can be incorporated into building better global prediction models of climate. This dissertation investigates the chemical composition of ultrafine particles across the Amazon Basin, commonly referred to as the "green ocean," and over marine environments, or the "blue ocean."

In Chapter 2, we measured the composition of ultrafine particles in the Amazon Basin using ThermalDesorption Chemical Ionization Mass Spectrometry (TDICMS) during the Green Ocean Amazon (GoAmazon2014/5) field experiment. The most abundant compounds detected in the positive and negative ion modes were measured. Two time periods arose over a ten day period of analysis, related to air mass back trajectories bringing different air masses to the sampling location. The first sampling period, deemed the anthropogenic period due to air masses originating over a metropolitan area, was characterized by higher particle number concentrations and larger amounts of particulate bisulfate. The background period, characterized by air masses arriving to the sampling site from northern forested areas, had 3-methylfuran as the dominant species, a thermal decomposition product of a particulate-phase isoprene epoxydiol (IEPOX). Additional statistical analysis was performed to compare the sources and composition of ultrafine particles to larger submicron particles. Hierarchical clustering separated ultrafine particle chemical components from the submicron particle chemical components, indicating that different processes or sources impact ultrafine particle formation and growth compared to larger submicron-sized particles.

Next, in Chapters 3 and 4, we measured the composition of ultrafine particles from both primaryand secondary marine sources using TDCIMS analysis during the Sea Spray Chemistry and Particle Evolution (SeaSCAPE) experiment. Primary marine aerosol, known as sea spray aerosol, is directly emitted into marine environments through wave breaking and bubble bursting. Using coastal water obtained from Scripps Pier in San Diego, CA, primary sea spray was generated using a wave flume. The measured trends in inorganic, NaCl, and organic fractions were dependent on active biological activity, with the organic fraction peaking with the total abundance of heterotrophic bacteria. At low phytoplankton activity, ultrafine particulate mass was mainly comprised of NaCl. Positive ion fragments characteristic of polysaccharides and fatty acids likely were of bacterial origin, were measured in ultrafine particles but not in larger sea spray aerosol (∼100-200 nm). Additionally, in Chapter 4, we report the general composition of ultafine secondary marine aerosol during times of high biological activity and mass fractions of particle phase ammonium, sulfate, methanesulfonic acid (MSA), dimethylamine (DMA) and iodine. Secondary marine ultrafine particles were formed using a potential aerosol mass oxidative flow reactor and oxidizing gaseous emissions from the wave flue with ∼1 day equiv. aging of OH. These measurements were paired with gas phase measurements of volatile organic compounds (VOCs) directly emitted from the wave flume to assess the formation pathways of secondary marine aerosol. More ultrafine secondary marine aerosol was produced during times of high biological activity, when sulfur containing VOCs were at their highest, leading to roughly 40% of the mass fraction being composed of the TDCIMS calibrated species listed above. We hypothesize that particulate DMA and ammonium are neutralized by sulfuric acid, MSA and organic acids. The general composition of secondary ultrafine particles during peak biological activity suggest influence from nitrogen and sulfur containing organic species and low volatility organics that can contribute to new particle formation.