Atmospheric Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 197

induced dissociation chamber. A nano-DMA is used downstream for particle size
selection. Aerosols are charged and are then collected by electrostic deposition
onto a metal fi lament. Then the fi lament is slid from the collection position into the
evaporation-ionization chamber where it is resistively heated to evaporate the
collected aerosol. The desorbed molecules are ionized at atmospheric pressure by
proton transfer with protonated water clusters or oxygen anions formed by reac-
tions between

particles (emitted by a 231 Am source) and the buffer gas mixture.
Ions are then transferred to a triple quadrupole mass spectrometer for mass
analysis.

α

5.6.4.3 Nanoparticle Properties Related to Chemical Composition

Recently, tandem differential mobility analysers (TDMA) have been developed in
order to measure some nanoparticle properties that are related to their chemical
nature, such as the volatility (volatility tandem differential mobility analyser or
VTDMA) or their hygroscopicity (hygroscopicity tandem differential mobility
analyser or HTDMA), or both for the volatility and humidifi cation tandem dif-
ferential mobility analysers (VH-TDMA). Basically, these instruments use two
DMAs (or two SMPSs) in series. The fi rst one selects a certain aerosol size. This
monodisperse aerosol is then either heated (in the case of the VTDMA) or humidi-
fi ed (in the case of the HTDMA) before entering the second DMA that is scanned
in order to measure the entire size distribution of processed aerosols. The concen-
tration of the monodisperse aerosol is monitored using a condensation particle
counter (CPC). These instruments give useful information on nanoparticle proper-
ties that may be climate and/or health-relevant. Information on aerosol mixing
properties (Biswas et al. , 2007 ; Philippin et al. , 2004) and some chemical composition
insights can be inferred by comparison with evaporation curves of known com-
pounds (Sakurai et al. , 2003 ; Meyer and Ristovski, 2007 ) .
Ultrafi ne Organic Tandem Differential Mobility Analysers (UFO-TDMA) also
exist. These instruments measure the ethanol uptake of particles of a certain size
(selected by a fi rst DMA). These particles are introduced into air mixed with
ethanol and their size changed is measured using a second DMA. The growth factor
of particles depends on their chemical nature and size. Comparison with current
knowledge on ethanol uptake permits inferences on the composition of atmo-
spheric NPs (Joutsensaari et al. , 2001 ).

5.7 Conclusions

The literature clearly indicates that road traffi c emissions dominate NPs emissions,
at least in the urban atmosphere. However, because of their small size, the current
knowledge of atmospheric NPs is primarily of number concentrations, and far less
is known of nanoparticle chemistry. This leads to diffi culty to apportion the contri-
butions of different sources. From the current knowledge, almost nothing is known
on the contribution of engineered NPs to atmospheric NPs. Also, emissions from
motor vehicles are not totally understood and further studies are clearly needed