Environmental Engineering Reference
In-Depth Information
Experimental Method
In the present study a bicycle equipped with a number of different instruments
(collectively called AeroFlex II) was used to measure aerosol concentrations in the
ambient environment and to evaluate personal exposure of cyclists. It is used here
to capture the time-activity exposure patterns of individuals in an urban transport
microenvironment. It consists of four different instruments: a GRIMM 1.108 Dust
monitor, a TSI P-TRAK, a commercial GPS and a video camera. The GRIMM
1.108 spectrometer is a portable environment dust monitor which can simultane-
ously measure PM1.0, PM2.5, PM10 and TSP. It has two optical sensors which
provide near real-time particle number concentration measurements at a maximum
logging rate of 1 min. The size range covered by the instrument is 0.3-20 mm over
15 channels. The design features of the GRIMM 1.108 provide ease of portability:
a rechargeable Li-Fe battery (providing 6 h of runtime) and 4 MB of internal data
storage
[3]
. This makes the GRIMM 1.108 readily deployable in the field and useful
for mobile measurements in the SHAPES project.
Ultrafine particle counts at 1-s resolution were made, using P-TRAK Ultra
fine Particle Counters (TSI Model 8525), for particles in the size range 0.02-1 mm.
The P-TRAK is a hand-held field instrument based on the condensation particle
counting technique using isopropyl alcohol. It has a relatively robust performance
while in motion, rapid warm-up, battery-powered, and it has an operation time
which is longer than more sophisticated instruments. The P-TRAK has the ability
to detect high concentrations (maximum detectable limit: 500,000 cm
−3
). Moreover,
it has a high data-logging resolution and a fast response time
[3]
.
Initial pilot tests revealed that the P-TRAK was rather sensitive to shocks leading
to temporary gaps in the data collected. This was circumvented by designing a shock
absorbing suspension and by manually bypassing the electronic shock detection
mechanism. This final set-up was used for all later measurements.
All measurements discussed in this paper were executed while cycling in real
traffic in and around the city of Mol, Belgium. A test trajectory was chosen that
includes a cycling track parallel to a major regional road N18 (two lanes, ~13,000
vehicles/day including buses and trucks, 70 km/h speed limit). The cycling lane is
between 1.8 and 2 m wide and is mostly separated from the road to the left by a 1.8 m
wide parking lane except at a signalized intersection (see Fig.
1
). There is also some
traffic on parking places around the shops situated to the right of the cycling track.
During the test there was a light wind blowing from NW at a 30° angle to the
road (which is oriented N-S). Meteorological data was not measured at the site
shown in Fig.
1
, but at the nearby VITO campus.
A first set of validation tests was conducted to test the reliability of the P-TRAK
instruments, as well as the set-up on the bicycle. Two P-TRAK instruments were
carried in a pannier and supplied with sampled air through two tubes of variable
length fitted to an extendible post so that any sampling height and direction could
be chosen (see Fig.
2
).
It was first tested whether the two available P-TRAK instruments can provide
identical results when sampling tubes are placed at the same location (Fig.
2
a).
