Atmospheric Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 195

Table 5.3 Summary of the characteristics of the main two classes of aerosol mass
spectrometer.

Laser-based Methods Thermal-based Methods

Principle Use of one or two lasers to

both vaporize and ionize
individual atmospheric
particles

Use of thermal vaporization of
individual or collected particles
followed by various ionization
techniques

Main
characteristics

Single particle analysis,
mixing states

One aspect of the chemical
composition of a single particle,
or, chemical composition of an
ensemble of particles

Species measured Analysis of inorganic, organic

compounds (organic
carbon, sulfates, nitrates,
sea salt, dust, metals etc.)
Aliphatic organic compounds
not detected

Suitable for semi-volatile aerosol
components (NH 4 NO 3 ,
(NH 4 ) 2 SO 4 , organic compounds)
Not suitable for elemental carbon,
sea salt and crustal material

Main advantages
or
disadvantages

Qualitative data, not
quantitative
Incomplete vaporisation (more
sensitive to species on
surface than in the core)
Matrix effects (interaction
between individual chemi-
cal components during the
combined desorption and
ionisation processes)

Quantitative detection of chemical
composition
Non-refractory species (see above)
not measured
Size of particles is not measured
except if a DMA is used in series,
or if the Aerodyne AMS is used
in the Particle time-of-fl ight mode

Examples of
Aerosol Mass
Spectrometers
used for the
measurement of
nanoparticles

UF-ATOFMS (Ultrafi ne
Aerosol Time-of-Flight Mass
Spectrometer): Su et al. ,
2004
RSMS (Rapid Single-Particle
Mass Spectrometry): Lake
et al. , 2003

TDPBMS (Thermal Desorption
Particle Beam Mass
Spectrometer): Tobias et al. , 2000
Aerodyne AMS (Aerodyne Aerosol
Mass Spectrometer):
Jayne et al. , 2000; Drewnick et al. ,
2005; DeCarlo et al. , 2006
TDCIMS (Thermal Desorption
Chemical Ionization Mass
Spectrometer): Voisin et al. , 2003

particles. This allows single particles between 50 and 300 nm to be sized and detected.
However, the ' hit ' rate is higher than 80% for particles larger than 120 nm but
dramatically drops to 55% for 95 nm particles (Su et al. , 2004 ). Additionally, the
particle detection effi ciency was found to be 0.3% for 95 nm polystyrene latex
spheres (Su et al. , 2004 ).

Thermal - b ased m ethods
Particles are focused onto a heated element that continuously vaporizes the volatile
fraction of the impacting particles that are subsequently ionized by electron ioniza-
tion (ARI AMS; TDPBMS) or by chemical ionization (TDCIMS).