Atmospheric Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 165

7

7 90

80

6

6

70

5

y = 0.0801x + 3.1296
R 2 = 0.71

5

60

4

50

4

40

3

R 2 = 0.73

30 3

2

20

2

1 N(11-30nm)/(100-450nm)

RH (%)

10

0 0 1

02468 0 2 4 6 8 0
Wind speed (knots)

0 5 10 15 20 25

Temperature (Celsius degree)

(a) (b)

Figure 5.4 (a) Relationship between the temperature and the ratio of integrated particle
counts from 11 to 30 nm to integrated particle counts from 100 to 450 nm; also presented
is the relationship between the relative humidity and the temperature. (b) Relationship
between the wind speed and the ratio of integrated particle counts from 11 to 30 nm to
integrated particle counts from 100 to 450 nm. (Reprinted from A. Charron and R.M.
Harrison, Primary particle formation from vehicle emissions during exhaust dilution in the
roadside atmosphere, Atmospheric Environment , 37 , 4109-19. Copyright 2003, with permis-
sion from Elsevier.)

distance of 0.45 metres behind the tailpipe. Rö nkk ö et al. (2007) showed that the
nucleation mode from a Euro IV heavy duty diesel is formed after 0.7 seconds
residence time in the atmosphere. Ambient temperature seems to mainly affect
particles smaller than 30-40 nm (Charron and Harrison, 2003; Olivares et al. , 2007 ),
which are almost entirely volatile (Kuhn et al. , 2005 ; Biswas et al. , 2007 ). Olivares
et al. (2007) also observed a signifi cant relationship between particles smaller than
20 nm and the relative humidity that was not observed by Charron and Harrison
(2003), while Charron and Harrison (2003) observed that increases in wind speed
increased the abundance of particles smaller than 30 nm in diameter relative to
particles greater than 100 nm in diameter, presumably because of the greater dilu-
tion and lower condensation sink (Figure 5.4b).
Du and Yu (2006) investigated the role of H 2 SO 4 - H 2 O binary homogeneous
nucleation in the formation of NPs in the vehicular exhaust. They demonstrated
that for vehicles running with fuel with high sulfur content (330 ppm), this signifi -
cantly infl uences new particle formation, especially at low temperature and high
relative humidity. They also showed that nanoparticle formation is signifi cant even
with fuel with low sulfur content (50 ppm). Another approach to modelling of par-
ticle exhaust emissions (Vouitsis et al. , 2005) showed that a possible mechanism for
new particle formation in diesel exhaust is the nucleation of sulfuric acid followed
by the condensation of hydrocarbons on sulfuric acid- water nuclei.
Many laboratory experiments have demonstrated that the nucleation mode (10-
40 nm) originates from the nucleation of sulfates over/within the oxidation catalyst