Atmospheric Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 164

1600 rpm 50% load

1.60E+09
1.40E+09

run 1 total dr=1090

1.20E+09

run2 total dr=54

1.00E+09

run3 total dr=28

8.00E+08
6.00E+08

4.00E+08

2.00E+08

0.00E+00

0 . 0 0 . 0 0 . 1

Dp ( µ m)

Run Dilution Number concentration Volume concentration

(#/cm 3 )
7.3E+08
3.0E+08
2.9E+08

( µ m 3 /cm 3 )
2.0E+04
1.9E+04
2.3E+04

ratio
1080
54
28

1
2
3

Figure 5.3 Comparison of particle size distribution measured at different dilution ratios at
engine speed 1600 rpm and 50% load. (Harrison, R. M., (2007), Nanoparticles in the atmo-
sphere, Nanothechnology: consequences for human health and the Environment, Issues in
Environmental Science and Technology , 24 , 35-49. Reproduced by permission of the Royal
Society of Chemistry. Adapted from Shi and Harrison (1999).)

Such dilution ratios in laboratory dilution tunnel experiments caused a decrease of
the particle size and an increase of the particle numbers while the overall volume
of particulate matter did not change signifi cantly. This is illustrated in Figure 5.3
(from Harrison (2007) adapted from the work of Shi and Harrison (1999)). Rö nkk ö
et al. (2007) confi rmed the observations of Shi and Harrison; while the comparison
of Giechaskiel et al. (2005) between laboratory (partial fl ow sampling system with
constant sampling conditions) and on-road measurements for diesel Euro III pas-
senger showed similar results for both sampling conditions despite the different
dilution ratio, sampling temperature and residence time of the aerosol in dilute
conditions.
While in situ and modelling studies have shown that particle number concentra-
tions measured at roadside sites depends on ambient temperature (Charron and
Harrison, 2003; Gidhagen et al. 2004b ; Janh ä ll et al. , 2004 ; Olivares et al. , 2007 ) as
illustrated in Figure 5.4a, many laboratory chassis dynamometer studies have not
found any infl uence of the sampling temperature (Mathis et al. , 2005 ; Giechaskiel
et al. , 2005 ; Casati et al. , 2007). In the real-world atmosphere, the process involved
is likely to be nucleation after mixing with the ambient air, as demonstrated by
Charron and Harrison (2003) and Olivares et al. (2007) . Accordingly, R ö nkk ö et al.
(2006) showed that the nucleation mode is formed within fi ve metres of the moving
vehicles and Uhrner et al. (2007) found the highest particle number counts at a