Article

Physicochemical and redox characteristics of particulate matter (PM) emitted from gasoline and diesel passenger cars

Department of Civil and Environmental Engineering, University of Southern California, 3620 S. Vermont Avenue, Los Angeles, CA 90089, USA; Laboratory of Applied Thermodynamics, Aristotle University, Thessaloniki 54124, Greece; Center for Occupational and Environmental Health, University of California, Los Angeles, CA 90095, USA
Atmospheric Environment DOI:10.1016/j.atmosenv.2006.06.018 pp.6988-7004

ABSTRACT Particulate matter (PM) originating from mobile sources has been linked to a myriad of adverse health outcomes, ranging from cancer to cardiopulmonary disease, and an array of environmental problems, including global warming and acid rain. Till date, however, it is not clear which physical characteristics or chemical constituents of PM are significant contributors to the magnitude of the health risk. This study sought to determine the relationship between physical and chemical characteristics of PM while quantitatively measuring samples for redox activity of diesel and gasoline particulate emissions from passenger vehicles typically in use in Europe. The main objective was to relate PM chemistry to the redox activity in relation to vehicle type and driving cycle. Our results showed a high degree of correlation between several PM species, including elemental and organic carbon, low molecular weight polycyclic aromatic hydrocarbons, and trace metals such as lithium, beryllium, nickel and zinc, and the redox activity of PM, as measured by a quantitative chemical assay, the dithiothreitol (DTT) assay. The reduction in PM mass or number emission factors resulting from the various engine configurations, fuel types and/or after-treatment technologies, however, was non-linearly related to the decrease in overall PM redox activity. While the PM mass emission rate from the diesel particle filter (DPF)-equipped vehicle was on average approximately 25 times lower than that of the conventional diesel, the redox potential was only eight times lower, which makes the per mass PM redox potential of the DPF vehicle about three times higher. Thus, a strategy aimed at protecting public health and welfare by reducing total vehicle mass and number emissions may not fully achieve the desired goal of preventing the health consequences of PM exposure. Further, study of the chemical composition and interactions between various chemical species may yield greater insights into the toxicity of the PM content of vehicle exhaust.

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Keywords

adverse health outcomes
 
chemical composition
 
desired goal
 
diesel particle filter
 
DPF vehicle
 
DPF)-equipped vehicle
 
environmental problems
 
gasoline particulate emissions
 
health risk
 
low molecular weight polycyclic aromatic hydrocarbons
 
mass emission rate
 
public health
 
quantitative chemical assay
 
redox activity
 
times higher
 
total vehicle mass
 
various chemical species
 
various engine configurations
 
vehicle exhaust
 
vehicle type