Review of diesel particulate matter sampling - Department of ...

• Light absorption cross sections for diesel particles observed in this study ranged from 5.7
to 6.1 m 2
/g and did not seem related to particle size. Light scattering cross sections
ranged from 1.5 to 3.9 m 2 /g and increased with particle size. Thus, coagulation growth
should not have a strong influence on light absorption cross sections but may increase the
light scattering cross sections of diesel particles as they age in the atmosphere.
Table 9 summarizes the properties of the aerosol size distributions measured in this study.
The range of N/VT (number of particles divided by EAA volume concentration) ratio (2,300
to 62,000) is similar to the one reported by Whitby, et al. (1975). Kittelson (1998a)
summarizes the data from the Kittelson, et al.(1988) study and additional data from the
University of Minnesota and others in table 10. It is clear from these tables that N/VT ratio
and thus the number of particles emitted per unit mass of particulate matter are highly
variable. The results suggest that N/VT ratios in the range of 50,000 to 60,000 part./μm 3 (or,
assuming spherical, unit density particles, 5 to 6 x 10 16 particles per gram of emitted particle
mass) are probably not uncommon for older diesel and SI engines under highway cruise
conditions. This is consistent with the N/VT ratio of 26,000 (Kittelson, et al., 1988) observed
over a rural freeway under mixed traffic conditions. This ratio is lower than source levels
because of dilution with aged ambient aerosol and coagulation. The values of 120,000 to
360,000 observed by Bagley, et al. (1996) are significantly higher than reported for other
engine types. The only way such a high N/VT ratio was produced at the University of
Minnesota was when a diesel engine equipped with a catalyst in an off-design was operated in
the laboratory under high load condition that led to significant sulfate formation. This led to
an N/VT ratio of 400,000.
Table 9. Properties of diesel exhaust size distributions (Kittelson, et al. 1988)
Property Ccp /Ct m/VT
g/cm 3
N/VT
part/μm 3
VN/VT Ec DGVn μm
DGVa μm
Range 0.12 - 0.2 1.2 - 2.2 2,300 - 0 - 0.35 0 - 0.38 0.022 - 0.19 - 0.34
62,000
0.032
Typical
value
0.15 1.2 NA NA NA 0.025 0.25
Ccp /Ct m/VT
Mass fraction of particles with aerodynamic diameters greater than 0.9 um.
Submicron filter mass concentration divided by EAA volume concentration.
N/VT Number of particles divided by EAA volume concentration.
VN/VT Volume fraction in the nuclei mode.
Ec DGVn DGVa NA
Solvent extractable fraction.
Geometric volume mean diameter of nuclei mode.
Geometric volume mean diameter of accumulation mode.
Highly variable so that defining a typical value was not appropriate.
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