Quantification of black carbon mixing state from traffic: implications for aerosol optical properties
- 1Department of Chemistry, University of Toronto, Toronto, Ontario, Canada
- 2Southern Ontario Centre for Atmospheric Aerosol Research, Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario, Canada
- 3Department of Chemistry and Environmental Research Institute, University College Cork, Cork, Ireland
- 4Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, Urbana, USA
- 5Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, USA
- anow at: Air Monitoring and Transboundary Air Sciences Section, Environmental Monitoring and Reporting Branch, Ontario Ministry of the Environment and Climate Change, Toronto, Ontario, Canada
Abstract. The climatic impacts of black carbon (BC) aerosol, an important absorber of solar radiation in the atmosphere, remain poorly constrained and are intimately related to its particle-scale physical and chemical properties. Using particle-resolved modelling informed by quantitative measurements from a soot-particle aerosol mass spectrometer, we confirm that the mixing state (the distribution of co-emitted aerosol amongst fresh BC-containing particles) at the time of emission significantly affects BC-aerosol optical properties even after a day of atmospheric processing. Both single particle and ensemble aerosol mass spectrometry observations indicate that BC near the point of emission co-exists with hydrocarbon-like organic aerosol (HOA) in two distinct particle types: HOA-rich and BC-rich particles. The average mass fraction of black carbon in HOA-rich and BC-rich particle classes was < 0.1 and 0.8, respectively. Notably, approximately 90 % of BC mass resides in BC-rich particles. This new measurement capability provides quantitative insight into the physical and chemical nature of BC-containing particles and is used to drive a particle-resolved aerosol box model. Significant differences in calculated single scattering albedo (an increase of 0.1) arise from accurate treatment of initial particle mixing state as compared to the assumption of uniform aerosol composition at the point of BC injection into the atmosphere.