Laboratory studies of black carbon particles: characterization and atmospheric processing

 

Authors

Timothy B Onasch — Aerodyne Research, Inc.
John T Jayne — Aerodyne Research, Inc.
Paul Davidovits — Boston College
Leah R Williams — Aerodyne Research Inc

Andrew Thomas Lambe — Aerodyne Research, Inc.
Adam Thomas Ahern — Aerodyne Research, Inc.

Ed Fortner — Aerodyne Research, Inc.
David Croasdale — Boston College

Category

Aerosol Properties

Description

Black-carbon-containing soot particles generated by incomplete combustion processes have a significant, though highly uncertain, effect on the direct (and indirect) radiative forcing of the global climate. The uncertainty in the climatic effects of soot particles is due to several important factors: (1) poorly understood rates of emission from various combustion sources (i.e., biomass burning, diesel engines, etc.), (2) highly irregular shapes of emitted soot particles (i.e., fractal-like) that can affect their atmospheric lifetimes, surface areas, and optical properties, (3) poorly quantified rates of atmospheric processing (e.g., hydrophobic into hydrophilic), and (4) rates of deposition. All these uncertainties are complicated by the lack of measurement techniques that can unambiguously measure soot particle chemical, physical, and optical properties. We are currently approaching this problem by developing new instrumentation for characterizing ambient soot particles and by studying soot particle properties in the laboratory. We have recently developed the Soot Particle–Aerosol Mass Spectrometer (SP-AMS). The SP-AMS utilizes an intracavity laser to selectively vaporize black carbon- and metal-containing particles, allowing the measurement of black carbon mass loading and size distributions, as well as measurement of the mass and chemical composition of any coating material (e.g., primary organic compounds and secondary organic and inorganic aerosol condensate). The measurement capabilities of the SP-AMS are currently being characterized in the laboratory and field. Results of these studies will be presented. We are also conducting laboratory studies of the physical, chemical, and optical properties of black carbon particles as a function of oxidation and condensational processes. Results from the Mexico City MILAGRO 2006 study indicate that soot particles can be rapidly processed in urban environments via secondary aerosol coatings, though it is unclear how these processes differ for primary soot particle sources located in urban and rural environments. Our current studies focus on the heterogeneous oxidation of “fresh” soot particle surfaces and the effects on particle chemical, physical, and hygroscopic properties. These studies set the baseline for atmospherically relevant studies on the effects of soot particle processing using well-characterized, laboratory-generated secondary organic and inorganic aerosol coatings.