Source apportionment of Arctic and remote marine carbonaceous aerosols
Carbonaceous aerosols are critical, short-lived climate forcers (SLCFs) that play complex roles in the climate system through their interaction with solar radiation, cloud nucleation, and are also a major contributor to air pollution. Globally and within the Arctic, changing aerosol burden associated with the decline of sea ice, shifts in the productivity of marine and terrestrial ecosys-tems, wildfire, and anthropogenic activities, remains an important uncertainty for projections of future climate change. To develop and evaluate effective air quality and climate change mitiga-tion policy, we urgently need a better understanding of emissions sources. An important step forward in unraveling the complexity of carbonaceous aerosols lies in the analysis of specific aerosol fractions that have different emissions sources, lifetimes, and cli-mate- and health impacts. A minor component with significant climate and health implications is black carbon (BC), a light absorbing SLFC emitted directly through incomplete combustion that leads to increased air column temperatures, accelerated ice and snow melt, shifts in cloud for-mation, cover, and lifetime, and have adverse effects on human health. The vast majority are or-ganic carbon (OC) aerosols, that are light-scattering, also emitted through combustion processes, and formed secondarily in the atmosphere. In this thesis, I combine OC/BC analysis with stable (12C, 13C) and radioactive (14C) carbon isotope data to improve our understanding of BC and OC sources (fossil vs. modern and terrestrial vs. marine) and their spatiotemporal variations within the High Arctic, which are considered primarily marine. I also explore aerosol composition in cur-rently understudied marine source regions. Despite significant history of Arctic aerosol monitoring networks and power of isotopic (and specifically 14C data) for source attribution, consistent 14C observations of Arctic aerosol remain sparse. This is largely driven by the small sample sizes of aerosol collected in remote envi-ronments. To make such data more readily accessible for current and future monitoring networks, I evaluate the efficacy of the ECT9 protocol, a temperature protocol designed to physically sepa-rate and trap OC and BC microsamples (<100 µg C) for accurate δ13C and 14C analysis. This is done by measuring the 14C content of individual and mixed OC and BC standards of varying sizes to quantify the extraneous carbon incorporated throughout the analytical process and the efficacy of OC/BC physical separation. The total modern and fossil extraneous carbon incorpo-rated by the set-up was 0.9±0.45 and 0.4±0.2 µg C respectively. The ECT9 technique was found effective at physically separating exclusively non-refractory OC and highly refractory BC and can be applied directly to monitoring networks using this protocol to quantify OC/BC concentra-tions. I utilize the ECT9 protocol to quantify BC concentrations and fossil fuel contribution to BC in total suspended particulates (TSP) and snow collected at the Dr. Neil Trivett Global At-mosphere Watch Observatory at Alert, Nunavut Canada, a long-term monitoring facility, over the course of one year (2014-2015). I determine the seasonal cycle of fossil fuel source contributions to show that BC is primarily dominated by fossil sources throughout fall- spring (47-70% fossil) and have major geographical sources from the Russian Arctic sector, though long-range contribu-tions from Asia cannot be excluded. Additionally, summer BC (20-52% fossil) is dominated by biomass burning in the North American Arctic sector as shown by GFED v4.1 Summer 2014 bi-omass burning emissions and enriched 14C values. BC in snow was enriched relatively to BC in TSP, though this effect was not homogeneous (53-88% biomass). High biomass burning contribu-tions in snow BC suggests wet deposition may be a key pathway for long-range transport of bi-omass burning emissions from the upper troposphere. Furthermore, I explore the various marine and terrestrial sources to OC aerosol across the northern Pacific and the Arctic Ocean. I combine dual isotopes (13C, and 14C) in a multi-source model to calculate and quantify the contributions from surface marine refractory dissolved organ-ic carbon (RDOC), fresh biomass, and liquid fossil to ambient aerosol. The data shows that re-mote marine aerosol is dominated by RDOC in the Pacific (90% RDOC) and to a lesser extent in the Bering Sea (47% RDOC). This work suggests marine RDOC and fresh biomass are important contributors to marine OC and may play an important role in future Arctic climate change. Together, my dissertation research established new analytical capabilities, produced criti-cal benchmark dataset, and advanced our understanding of carbonaceous aerosol in the rapidly changing Arctic.