AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Characterizing the Efficiency of the SP-AMS for Measuring Black Carbon in Organic Coated Particles
MEGAN D. WILLIS, Alex K. Y. Lee, Jonathan Abbatt, University of Toronto
Abstract Number: 84 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Black carbon (BC) containing aerosol affects air quality, impacts human health, and can have a significant effect on regional and global climate. Freshly emitted BC particles tend to be small (aggregates of ~10-50 nm BC spherules), but quickly grow and become mixed with other species through condensation and coagulation. The Soot-Particle Aerosol Mass Spectrometer (SP-AMS) is a new instrument that combines the operating principles of the Single Particle Soot Photometer with the Aerodyne High-Resolution Time-of-Flight AMS, making quantification of BC and its non-refractory coating materials possible. The goal of this work is to assess the ability of the SP-AMS to accurately quantify BC inclusions of atmospherically relevant sizes in organic coated particles. This issue is addressed in two ways. First, we examine whether small BC inclusions (e.g. down to 50 nm) in organic-rich particles are being detected with the same efficiency as larger, bare BC particles (e.g. 300-400 nm). Secondly, we examine whether BC and its associated coating materials are being quantified accurately relative to each other. The ionization efficiency for BC relative to nitrate was measured for small cores in organic rich particles (0.40 ± 0.10) and for larger, bare BC particles (0.25 ± 0.05), yielding an average value of 0.35 ± 0.10. The difference in sensitivity may be due to a combination of factors, including differences in particle collection and transmission efficiency. These measurements demonstrate that the SP-AMS is capable of detecting small BC inclusions with the same efficiency as larger BC particles previously used for instrument calibration. In addition, the SP-AMS can accurately quantify the fraction of BC in organic rich particles down to 3% BC by mass.