Urban Aerosol in a Light Industrial Area – Particle Size
Distribution and Number Concentration Measurements
in the Submicron Range
Axel F. Zerrath, Oliver F. Bischof
TSI GmbH, Aachen, Germany
Presented at the European Aerosol Conference, 28th August – 1st September 2005
Introduction
Results
Urban air quality has been under increased
scrutiny over the last few years. With the
beginning of the year 2005 a new EU regulation
limits the fine particle fraction of particulate
matter in ambient air. Urban air consist of a
significant fraction of submicrometer, and
ultrafine particles in particular, which make a
small contribution to the particulate mass, but are
said to be associated with a number of health
effects (see also figure 5). The most significant
adverse health effects have been reported for
areas with the highest levels of particle
concentrations. Industrial areas within European
cities with their increased traffic and industrial
emissions are typical examples for those high
levels.
Size distributions show the typical pattern of
urban aerosol reported in several studies
(Koponen et al., 2004). Number distributions are
dominated by particles below 200 nm but
individual events with a distinct mode below 50
nm occur. Both effects appear to be traffic
related. Figure 1 shows an example from April.
Figure 3: Particle number concentrations
measured by CPC, WCPC and SMPS.
Location
An urban, light industrial area in the city of
Aachen (Germany) was chosen for the
measurements. The measurement site was
located at a distance of about 50 m from a road
leading to a municipal vocational training center,
only 200 m from the A544 freeway and just
opposite the bus depot of the city’s public
transport company (ASEAG).
Figure 1: SMPS size distribution of urban
aerosol on a typical weekday in April 2005.
The measurement site is situated nearby the
main bus depot of a public transport company.
Buses leaving the depot in the morning seem to
be the likely reason for the frequent upcoming
particle concentration starting at about 4:30 am.
Figure 2 shows typical background aerosol
compared to a traffic-related event measured.
Figure 4: Correlation of WCPC to CPC in singlecount mode. Both CPCs with equal lower cut point
of 10 nm.
Finally, to account for both submicron and coarse
particles, a newly developed data merging
software was used to combine SMPS and APS
data. The results are shown in figure 5.
The measurements were done to compare the
performance of different, state-of-the-art as well
as newly developed aerosol measurement
instruments during 24/7 monitoring of urban
aerosol.
Instruments
Three physical parameters of the urban aerosol
were chosen for the measurements: number
concentration, size distribution, and diameter
concentration, all measured simultaneously.
Instruments used included:
• Single-box SMPS (scanning mobility particle
sizer), TSI model 3034
• Water-based CPC (condensation
counter), TSI model 3785 and 3782
particle
• CPCs, TSI models 3010, 3022A and 3025A
• Electrical Aerosol Detector (EAD), TSI 3070A
• APS (aerodynamic particle sizer), TSI 3321
Measurements were performed in April, June
and July 2005. An electropolished, stainless
steel tube was used to transport the aerosol from
outside the building to the instruments. A flow
splitter and equal lengths of conductive silicone
tubing transported the aerosol to the instruments.
Figure 2: Size distribution of typical background
level and particle event.
The total number concentrations from SMPS,
CPC and WCPC (e.g. in figure 3) measured were
between ~5,000 P/cm3 at night-time and up to
100,000 P/cm3 during events. We observed a
good correlation between the instruments well
within the specified accuracy. Data from the
WCPC is real-time corrected for coincidence in
the instrument’s firmware, and therefore slightly
below the concentration measured by the
butanol-based CPC. Both CPCs have a D50%
cut-off below the SB-SMPS size range. Due to
the significant number concentrations below a Dp
of 10 nm, the SB-SMPS total number
concentration is below the values of the CPCs.
Correlating data from a CPC and a WCPC with
identical lower cut-points in single count mode
results in an agreement above 91% (figure 4).
Figure 5: Number size and mass distribution from
merged APS and SMPS data.
Conclusions
All instruments used proved their reliability for
continuous measurements of urban aerosol. The
concentrations derived from the SB-SMPS agreed
well with the ones measured by stand-alone
CPCs. No differences between CPCs using water
and butanol as the working fluid were observed.
References
Koponen, I.K. et al. Comparison of Aerosol
Number Size Distributions between Roadside and
Urban Background Sites.
Abstracts of EAC 2004.