Diesel Nucleation Mode Particles: Semivolatile or Solid?

Although the preponderance of current data points to semivolatile diesel nuclei particles composed of sulfuric acid and heavy hydrocarbons, the question remains as to what extent, if any, they contain solid cores. We present evidence here of a “solid” particle nucleation mode that accompanies normal...

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Bibliographic Details
Published in:Environmental science & technology 2008-11, Vol.42 (21), p.7957-7962
Main Authors: Filippo, Andrea De, Maricq, M. Matti
Format: Article
Language:English
Subjects:
Airborne particulates
Applied sciences
Diesel fuels
Electric currents
Environmental Processes
Exact sciences and technology
Gasoline - analysis
Hydrocarbons
Models, Chemical
Nanoparticles
Particle Size
Particulate Matter - chemistry
Pollution
Static Electricity
Sulfur
Sulfuric acid
Temperature
Vehicle Emissions - analysis
Volatilization
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Summary:Although the preponderance of current data points to semivolatile diesel nuclei particles composed of sulfuric acid and heavy hydrocarbons, the question remains as to what extent, if any, they contain solid cores. We present evidence here of a “solid” particle nucleation mode that accompanies normal soot emissions in the case of two modern light-duty diesel vehicles run with ultralow sulfur fuel. This mode is most prominent at idle, but also appears at speeds below ∼30 mph, and is highly sensitive to the level of exhaust gas recirculation (EGR). The nuclei particles are examined for their volatility and electrical charge. In stark contrast to “conventional” nuclei particles, they remain nonvolatile to >400 °C and exhibit a bipolar charge with a Boltzmann temperature of 580 °C. Their nonvolatile nature rules out sulfate and heavy hydrocarbons as primary constituents, and their electrical charge requires formation in a high-temperature environment capable of generating bipolar ions. This suggests that “solid” nuclei particles form during combustion but remain distinct from soot particles, analogous to what has been found recently in flames. As concerns about potential emissions of nonvolatile nanoparticles have already surfaced, an important conclusion of this study is that diesel particulate filters remove the “solid” nucleation mode with an efficiency comparable to soot.
ISSN:0013-936X
1520-5851
DOI:10.1021/es8010332