Atmospheric Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 180

The same conclusion could be drawn from other studies. As an example, Harrison
and Jones (2005) reported number concentrations of particles larger than 7 nm at
a number of British locations where the same instruments were deployed. Strong
gradients were found between the industrial site of Port Talbot (not directly infl u-
enced by traffi c emissions), the urban centres of Glasgow, London, Birmingham,
Manchester and Belfast and the street canyon of Marylebone Road, London, which
shows by far the highest particle number concentrations (Figure 5.6). Particle
number concentrations at the background sites were typically around 20 000 cm − 3 ,
while they reach 117 000 cm − 3 at Marylebone Road (Harrison and Jones, 2005). Note
that for rough comparison (another instrument is used), average particle number
concentrations of about 900 cm − 3 were measured at the mountainous (free tropo-
spheric) Jungfraujoch site, Switzerland (Van Dingenen et al. , 2004 ). Weijers et al.
(2004) observed a relationship between particle number concentrations and density
of population in The Netherlands, a result that again highlights the strong contribu-
tion of traffi c sources.
Strong spatial variations of ultrafi ne particle number concentrations are also
observed at the urban scale. Number concentrations showed strong peaks in the
near vicinity of roads and highways with intensity depending on traffi c character-
istics (Weijers et al. , 2004). Particle number concentrations exponentially decrease
as the distance from the roadway increases (Zhu et al. , 2002) to reach their upwind
background concentration at distances that depend on the site characteristics (often
Figure 5.6 Seasonal infl uence on number concentration at various British sites. (Reprinted
with permission from R. M. Harrison and A. M. Jones, Multisite study of particle number
concentrations in urban air, Environmental Science and Technology , 39 , 6063-70. Copyright
2005, American Chemical Society.)