AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
The Mixing State of Urban Black Carbon: From Single Particles to an Ensemble View
ALEX K. Y. LEE, Megan D. Willis, Robert Healy, Jon M Wang, Cheol-Heon Jeong, Matthew West, Nicole Riemer, Greg J. Evans, Jonathan Abbatt, University of Toronto
Abstract Number: 19 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Black carbon (BC) particles emitted from incomplete fossil fuel combustion and biomass burning can result in a significant warming effect on climate. However, the magnitude of black carbon’s impact on the global scale remains highly uncertain and is closely related to its particle-scale physical and chemical properties. In this study, we quantify refractory black carbon (rBC) mixing state in an urban environment using both single particle and bulk measurements from an Aerodyne soot-particle aerosol mass spectrometer (SP-AMS). Cluster analysis of single particle data indicates that rBC is internally mixed with hydrocarbon-like organic aerosol (HOA) in two distinct particle classes: rBC-rich and HOA-rich particles that contain > 60% and < 10% rBC by mass, respectively. Assuming a core-shell particle structure, it is estimated that rBC-rich particles are thinly coated by HOA and have much larger rBC core sizes compared to HOA-rich particles. Positive matrix factorization (PMF) analysis of bulk SP-AMS measurements in a roadside environment demonstrate the presence of two traffic-related source profiles containing different mass fractions of rBC, in agreement with the single particle results. With the support of single particle observations, the PMF results indicate that ~90% of rBC and ~40% of HOA emitted from local sources are contributed by rBC-rich particles in an urban environment dominated by primary emissions. This work provides quantitative insight into the physical and chemical nature of BC-containing particles near emission sources and can be used as a basis for developing our understanding of BC mixing state and its evolution in the atmosphere. The impacts of mixing state on aerosol properties such as cloud condensation nuclei (CCN) activity and single scattering albedo (SSA) will be evaluated based on modeling results.