Soot Aerosols: Why are they important?
Thursday, October 15, 2009
Paul Davidovits, PhD is a Chemistry Professor at Boston College.
Abstract: Results of field and laboratory studies indicate that atmospheric soot aerosols contribute significantly to global warming through direct (absorption) and indirect (cloud condensation nuclei) effects. Soot particles consist of a black carbon core combined with a variable amount of condensed-phase material (organic and/or inorganic). The exact composition of the soot depends on combustion conditions, and the level of atmospheric conditioning the particles have undergone. Even though black carbon (BC) constitutes a small fraction of the total global aerosol mass burden, BC is estimated to contribute the equivalent of 1/4 of the warming caused by CO2. Regional heating effects are likely to be particularly important. Accurate in-situ measurements of the chemical, physical, and optical properties of soot particles are necessary to improve model estimates of the radiative forcing in the atmosphere due to black carbon. Toward this goal, an instrument inter-comparison study was conducted using the Boston College laboratory flame apparatus and particle characterization equipment. Methods used in the study, developed to measure the optical and physical properties of soot particles in real time, will be described. A pre-mixed flat flame burner operating at controlled fuel–to-air ratios produced stable and reproducible concentrations of soot particles with known morphologies and coatings (atmospheric conditioning). Twenty-six people representing 12 institutions participated in the project operating 6 mass- and 7 optical-based real-time instruments. The results of the study yielded information both about instrument performance and about physical, optical and chemical properties of soot particles.