Quantifying Aerosol Diversity of an Arctic Oil Field on a Single Particle Level

JUDY WU, Jun Liu, Matthew Gunsch, Jessica Mirrielees, Claire Moffett, Rebecca J. Sheesley, Qi Zhang, Swarup China, Kerri Pratt, University of Michigan

     Abstract Number: 370
     Working Group: Remote and Regional Atmospheric Aerosol

Abstract
As the Arctic rapidly warms, sea ice extent is decreasing, and oil and gas extraction are increasing. The emissions from these processes affect the distribution of chemical species across individual particles within an aerosol population, or chemical mixing state, which impacts properties such as reactivity and hygroscopicity, with implications for air quality and human health. In August – September 2016, the sources, chemical composition, and mixing states of atmospheric aerosols within an Arctic oil field (Oliktok Point, Alaska) were investigated using a suite of instrumentation. An aerosol time-of-flight mass spectrometer measured the real-time size and chemical composition of single particles. Aerosol particles measured in this study mainly included diesel soot, amine-containing organic sulfate particles, aged combustion aerosol, and sea spray aerosol; these particles were frequently internally mixed with sulfate and nitrate, indicative of secondary aerosol production within the oil field. Bulk mass concentrations of submicron non-refractory species were measured by a time-of-flight aerosol chemical speciation monitor, and black carbon was measured by an aethalometer. Additionally, scanning electron microscopy with energy-dispersive x-ray spectroscopy measured elemental ratios for the sea spray and mineral dust particles. Using a combination of the techniques mentioned above, we can quantify the contributions of these single-particle types and the overall diversity of PM₁ (particulate matter < 1 µm in diameter) to determine the mixing state index χ, a parameter representing how internally or externally mixed a particle population is at a given time, over the course of the field campaign. Here, we present the aerosol mixing state within oil field plumes, compared to background air, by examining the main aerosol species (sulfate, nitrate, ammonium, organic carbon, black/elemental carbon, chloride, sodium) over time. Accurate representation of atmospheric aerosol mixing state is important for air quality and climate modeling, which typically uses an internal mixing assumption.