VOLATILE METHYLATED SULFUR AND REACTIVE ORGANIC CARBON IN THE SPRING-TO-SUMMER MARINE ARCTIC ATMOSPHERE

Abstract

The emission and oxidation of trace gases in the atmosphere is a major control on the formation and growth of aerosols, but the wide array of organic trace gases are poorly characterized especially in remote environments.In this dissertation, we developed new chemical ionization methods and apply those newly developed methods to measure trace gases in the Arctic marine atmosphere. First, (Chapter 2) we optimized chemical ionization mass spectrometry instrument conditions for combining two reagent ions (NH4+ and H3O+) in a single instrument. We characterized NH4+ and H3O+ ionization in the laboratory, investigating the mass spectra from different known analytes, quantifying sensitivity, fragmentation, and humidity dependence. We then deployed our reagent ion switching chemical ionization mass spectrometer in a field setting at Manitou Experimental Forest Observatory in Woodland Park, Colorado. We demonstrated with a complex sample of mostly biogenic gas-phase organics (i.e., terpenes and terpenoids), that the two reagent ions are complementary. While H3O+ detects reduced species well and is a non-specific reagent ion, reduced fragmentation with NH4+ provides improved detection of oxygenates with higher selectivity. Next, we deployed our newly developed chemical ionization method onboard the Swedish icebreaker Oden in the Arctic marine atmosphere as part of the Atmospheric Rivers and the onseT of ice MELT (ARTofMELT) expedition. We applied our measurements obtained at the spring-to-summer transition (May/June) in the Fram Strait region (between Greenland and Svalbard) to investigate (Chapter 3) the role of sea ice regions as sources of the reduced volatile methylated sulfur species, dimethylsulfide and methanethiol, (Chapter 4) the importance of halogen initiated oxidation for the fate of dimethylsulfide prior to Arctic melt onset, and (Chapter 5) the composition and potential source regions of reactive organic carbon. We applied a combination of back trajectory analyses, a simple zero-dimensional kinetic box model, and a chemical transport model to test and understand the source regions and processes that shape our observations. We demonstrated that omitting sea-to-air emissions in sea-ice regions underpredicts dimethylsulfide and methanethiol concentrations and that halogen initiated oxidation dominated dimethylsulfide loss prior to ice melt onset. Finally, we found that gas-phase organics were likely sourced from sea-ice regions and that the organic composition measured at Oden changed over the spring-to-summer transition, with organic trace gases becoming larger and more saturated during the onset of summertime conditions. Finally, we end with a brief synthesis of the research and make suggestions for future work in addressing the uncertainties in the oxidation and emission of organic trace gases in the Arctic marine atmosphere.