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Faculty of Mechanical Engineering
Institute of Process Engineering and Environmental Technology
Research Group Mechanical Process Engineering
Dipl.-Ing. Lars Hillemann,
TU Dresden, Inst. of Process Engineering and Environmental Technology
Research Group Mechanical Process Engineering, D-01062 Dresden
Phone: +49 351 463 32914 Fax: +49 351 463 37058
Email: lars.hillemann@tu-dresden.de
Web:
http://www.mvt-tu-dresden.de
Aerosol mobility spectrometry based on
diffusion charging
L. Hillemann, A. Zschoppe and R. Caldow
In a particle sample characterized by mass the particles
contribute to this measure weighted by x
3
. Hence a mass
concentration is overemphasized by coarse particles whereas
the critical fraction of ultrafine particles is underpredicted.
This problem can be tackled by using number concentrations
to quantify the particle concentration in the environment.
Several available systems for the number concentration
measurement are designed for the lab and are not suitable
for monitoring networks.
Spectrometer setup
Inversion
Requirements
By combining the corona-jet-charger with a DMA and an electrometer, a new
aerosol spectrometer similar to an EAA and DMPS was developed. The
advantage of this device is its simple set-up and the stability and robustness
of the components. More problematic is the superposition of the mobility
spectra of different particle size fractions due to their broad charge
distribution. This leads to a lower size resolution compared to the SMPS.
However, it is sufficiently precise for environmental aerosol quantification in
air pollution networks.
[1]
Whitby, K. T., Clark, W. E. (1966). Tellus , 18, 573.
A measurement cycle delivers the mobility distribution of the particle-bound
electrical charge. The inversion problem to calculate the size distribution f(x) from
the measured current distribution g(y) is described by the Fredholm-equation.
The kernel data K(x,y) of the UFP-system is recorded
by a parallel quantification of a monodisperse aerosol
by SMPS, CPC and UFP.
particle deposition in the
respiratory system
Working range of the developed spectrometer
Set-up of an
aerosol spectrometer
Relation between particle size and
mobility for different charge states
Charger
Classifier
Detector
charging the
particles
classifying into
size classes
quantifying the
concentration
minimum
size
~ 20 nm
maximum
size
~ 800 nm
minimum
concentration
~ 1000 p/cm
3
PM 10 on
march 23
and march 24
Aerosol spectrometers combine an electrostatic classifier and an
electrometer to measure the mobility distribution of an aerosol. This
technique bases on the classification of charged particles in an electric field.
Accurate particle size detection requires a well-defined charge status of the
aerosol which is achieved by diffusion charging.
The inversion algorithm employed in the UFP 330 uses constraints like the typical
shape of an environmental particle size distribution and boundaries for the particle
size.
Charging of particles by means of an electrical
field or corona-generated ions has been
known for many years. Whitby and Clark
introduced the diffusion charging of an
aerosol by preventing the particles from
undergoing strong field charging. This
mechanism was used to produce a
monotonic decreasing relationship between
size and electrical mobility of the aerosol
particles [1].
Motivation
In March 2007 high PM-10-concentrations were observed in
Germany, caused by long range transport of coarse dust.
Fortunately no impact on human health was registered during this
time.
This illustrates the need for monitoring of ultrafine particles for the
relation of health effects to dust concentrations.
number and mass conc.
in march 2007
The demands for this purpose are:
• no radioactive source
• no butanol
• reduced data set
• easy operation
• low maintenance