Chemical Diversity of Tar Balls in Wildfire-Influenced Aerosol: A Single-Particle Analysis of the 2017 Pacific Northwest Fires
AMNA IJAZ, Kaitlyn J. Suski, Zezhen Cheng, Yuzhi Chen, Gourihar Kulkarni, Sijia Liu, Tania Gautam, ManishKumar Shrivastava, Jerome Fast, John Shilling, Swarup China, Alla Zelenyuk, Pacific Northwest National Laboratory
Abstract Number: 524
Working Group: Carbonaceous Aerosols
Abstract
The Pacific Northwestern US and Southwest Canada experienced extensive wildfires from mid-August through September 2017, offering a unique opportunity to study wildfire-influenced aerosol. Using complementary techniques, including a miniature single particle mass spectrometer, miniSPLAT, and a high-resolution aerosol mass spectrometer, HR-ToF AMS, we conducted a comprehensive investigation into the chemical composition and physical properties of sub-micron aerosol, focusing particularly on tar balls. We demonstrate that the wildfire-influenced plumes sampled here featured PM1 loadings of ~60 µg/m3, with aerosol being mainly carbonaceous and spherical, consistent with their microscopic images. This aerosol presented diameters ranging from 100 to 400 nm and densities between 1.35 and 1.45 g/cm3. Despite the predominantly organic and aged nature of aerosol, as revealed by the HR-ToF AMS, miniSPLAT identified eight distinct particle types with varying internal compositions of elemental carbon, potassium-related species, oxygenated organics, and polyaromatic hydrocarbons (PAHs). Notably, PAH-containing particle types were associated with larger sizes, i.e., dva > 300 nm, and were prevalent on the most polluted days. These particles were remarkably stable, retaining approximately 90% of their volume after 24 hours under both dry and humid conditions, indicating low volatility and high viscosity. The persistence of PAHs within these highly viscous particles suggests potentially extended atmospheric lifetimes and environmental impacts. Our findings provide insights into the complex physicochemical nature of wildfire-influenced aerosol and reveal that tar balls exhibit significant particle-to-particle chemical diversity that may influence their impact on radiation and clouds, as well as environmental fate.