Atmospheric Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 171

et al. , 2007). However, concentration levels reached in offi ces with printers and
without photocopiers were much lower than those measured in photocopy centres
(on average 6.5

1 0 3 c m − 3 ) (He et al. , 2007 ).
Exposure to NPs during a daily commute seems to be dominated by the exposure
to motor vehicle emissions. Similar to particle number size distributions measured
in street canyons, car in-cabin particle number size distributions were mostly
bimodal with peaks at 10- 30 nm and 50 -70 nm in diameter (Zhu et al. , 2007 ). Zhu
et al. (2007) demonstrated that the vehicle's ventilation particle fi lter offered an
in-cabin protection of about 50% for particles in the 7-40 nm size range and of
20-30% for particles above 40 nm. Unlike larger particles, no source of ultrafi ne
particles has been found in the London underground (Seaton et al. , 2005 ). Thus,
particle number concentrations were lower in the London underground than
outside and similar concentration levels were found on platforms and in train cabs
(Seaton et al. , 2005 ).

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5.2.1.3 Industrial Sources and Other Combustion Sources

Biswas and Wu (2005) reviewed research concerning stationary industrial sources
responsible for nanoparticle emissions. Various stationary sources were found to
emit NPs in large amounts, such as coal fi red combustion systems, incinerators, coal/
oil/gas boilers, smelters and residential combustors. Similar to vehicular emissions,
particle number size distributions depend on the composition of the fuel, on the
dilution process (residence time and dilution ratio) and on the concentrations of
larger particles that provide a large surface area for vapour condensation and
coagulation with smaller particles. This behaviour is consistent with that of semi-
volatile species, while metals were found to be in important concentrations in
particles smaller than 100 nm from stationary combustion sources (Tolocka et al. ,
2004a ; Dillner et al. , 2005 ).
Bond et al. (2006) compared ultrafi ne particle emissions from an old coal-fi red
heating plant and from an industrial boiler that burns natural gas and residual oil.
The number concentration maximum (3 1 0 8 c m − 3 ) in the exhaust of the industrial

boiler burning oil was about a factor of 30 greater than the highest value for natural
gas. The emissions of the brown-coal heating plant had number maxima at particle
diameters ranging between 50 and 100 nm, while the largest number concentrations
of natural gas and oil particle emissions occur in particle diameters below 10 nm.
Accordingly, very large concentrations of potassium and calcium were found in the
aerodynamic size range of 56-100 nm in aerosols measured in Houston, USA,
related to the emissions of a coal-fi red power plant. Two combustion plants in
Birmingham, UK, one burning gas and oil and the other associated with an incin-
erator, were found to be signifi cant and stable sources of NPs between 3 and 7 nm
(Shi et al. , 2001a ).
Particle number size distributions between 11 and 450 nm have been measured
since 1998 at the receptor site of Harwell in the rural Oxfordshire, UK. The activity
of a coal-fi red and gas burning power plant (coal-fi red power station of 2000 MW
and combined cycle gas turbine plant burning natural gas of 1400 MW) located 7 km
away did not infl uence particle number size distributions measured at the measure-

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