UK Consortium Project funded by the EPSRC

1
UK Consortium Project funded by the EPSRC S.
Arnold(12), H. ApSimon(1), J. Barlow(2), S.
Belcher(2), M. Bell(3), R. Britter(4), H.
Cheng(5), R. Colvile(1), A. Dobre(2), S. Kaur(1),
D. Martin(6), M. Neophytou(4), G. Nickless(6),
C. Price(6), A. Robins(5), D. Shallcross(6), R.
Smalley(3), J. Tate(3), A. Tomlin(3). (1)Imperial
College London (2)University of Reading
(3)University of Leeds (4)University of
Cambridge (5)University of Surrey (6)University
of Bristol.
INTRODUCTION The aim of the DAPPLE project is to
enhance understanding of dispersion processes,
over short distances, at a street canyon
intersection. This information will be used to
make improvements in predictive ability that will
enable better planning and management of urban
air quality, accidental and non-accidental
releases, and the development of safer more
sustainable cities. DAPPLE brings together a
multidisciplinary UK consortium undertaking
research in the field, wind tunnel, and via
numerical simulations in order to provide a
better understanding of the physical processes
affecting the flow of air, traffic, people and
their corresponding interactions with the
dispersion of pollutants. This poster introduces
the DAPPLE field measurements and a sample of the
preliminary results.
WIND FIELD RESULTS METEOROLOGY AND
POLLUTION The flow at the intersection during
oblique rooftop winds can be explained by the
linear superposition of the parallel and
perpendicular rooftop components the parallel
component giving the direction of channelling and
the perpendicular component driving the in-street
recirculation vortices (evidence for which can
also be seen in the CO data from the street
boxes, Fig. 3). The combination of the two wind
component effects can also be used to explain
in-street helical vortices (sometimes described
as reflection phenomenon). Fig. 4a. shows a
day when the rooftop winds (Site 10) change from
a positive (SSW before 1200) to a negative (W
after 1500) approach angle with respect to
Marylebone Road (rotated to be 0 degrees).
Despite the actual variation in wind direction
being small the change in the approach sign
results in a 180º reversal of the flow in
Gloucester Place (Site 5). Sites 2 5, due to
their constrained canyon locations, both exhibit
channelled flow with single peak directional
PDFs (not shown). Site 1 (Fig. 2) is more open
in westerly approach winds and produces a two
peak PDF (Fig. 4b) the flow switching between
Marylebone Road (0 - westerly) and Gloucester
Place (-100 - southerly).
Fig. 3. Street box data from the North (Site 3)
and South (Site 4) pavements, and the central
reservation (Site 2) of Marylebone Rd. Note, the
cross-street variation in CO in the afternoon
implying a street canyon vortex during oblique
rooftop winds.
Fig. 2. Site 1, ultra sonic anemometer and street
box on a lamppost in the central reservation of
Marylebone Rd.
Fig. 4b.
Fig. 4a.
Marylebone Rd

• FIELD CAMPAIGNS
• Two DAPPLE field campaigns, April-May 2003 and
  April-June 2004, were undertaken at the
  intersection of Marylebone Road and Gloucester
  Place, Westminster, Central London, UK.
  Marylebone Road is a 7 lane dual carriageway
  approximately 38 m wide running WSW-ENE and
  Gloucester Place is a 3 lane road approximately
  20 m wide which is one way to the North.
  Building heights vary between 10-30 m. Fig. 1.
  identifies the main DAPPLE measurement sites at
  the intersection. Data from these sites include
• Wind field up to 11 x 3-component ultrasonic
  anemometers were deployed at heights ranging from
  1.5180 m, within and above the street canyon
  intersection measuring the mean and turbulent (20
  Hz) flow (Fig. 2).
• Pollution levels 15 CO Learian street boxes
  were deployed in the intersection and surrounding
  streets between 4-10 m vertical pollution
  gradients of CO, CO2, O3 and PM2.5 were made at
  WCC between 0-15 m (Site 11)
• Personal exposure measurements of CO, PM2.5
  and ultra-fines were made by people carrying
  instrumentation through the study domain at
  different locations on the pavement and via
  different routes and modes of travel (Fig. 7a)
• Traffic flow manual traffic count validations
  of the SCOOT system were undertaken and will be
  developed into a micro-traffic flow simulation
  model
• Tracer releases inert tracers (SF6 and PMCH)
  were released in SSW winds from vehicles parked
  in York Street (Sites X1 X2) and from WCC roof
  (Site X3). Time series (10 x 3 mins bags) of air
  samples at 16 locations throughout the study area
  were used to track the tracers (Fig. 6).

Fig. 4a. Wind direction time series for the 9th
May 2003. Decomposition of the rooftop winds
(which change from SSW to W during the day) is
used to explain the in-street flows. Fig. 4b.
Directional PDF for Site 1. Note, the 2 peaks
would only be of even size for an approach flow
of 45 to Marylebone Rd lesser or greater angles
produce a dominance in Marylebone Rd or
Gloucester Pl, respectively.
Fig. 5a.
R 75 m, Thornton Place R115 m, WCC roof R115
m, WCC ground R120 m, Bickenhall St R200 m,
Marylebone Rd R200 m, Bickenhall Mansions R275
m, Baker Street
Note Below Fig. 1. has North in a conventional
vertical orientation. The poster background
image, taken from the BT tower (Site 17 _at_ 180 m),
is looking towards the DAPPLE site and so has an
approximate westerly orientation.
Fig. 5b.
Fig. 5a. Non-dimensional tracer concentrations
(C CUrefH2/Q, where C is the mean
concentration Uref is ref wind speed at WCC Site
10 H is average building height (22 m) and Q is
quantity of release (114 mg)) through time for 10
receptor sites. Fig. 5b.
Non-dimensional concentrations as a function of
separation R/H (where R is the straight line
fetch/distance).
Fig. 6. Blue tracer receptor box on Marylebone
Road (near site 3) looking SW towards the WCC
building.
MARYLEBONE RD
TRACER RELEASE RESULTS 15 MAY 2003 The
concentration of tracer decreases with increasing
fetch (R, which was between 75-275 m) from the
release site (Figs. 5a). There is an upper band
to the maximum tracer concentration as a function
of separation, Cmax XR-2 (Fig. 5b). This
relationship has also been documented in both the
DAPPLE wind tunnel experiments and the numerical
modelling results. The exact value of X in the
equation does however vary. During the release
the rooftop winds (Uref) were approx. 3 ms-1
hence the travel speed to WCC (R115 m) was
0.13Uref with a time of flight (tstart-t50conc.)
of 4.5 mins. There was rapid vertical mixing of
the tracer the roof top and ground level sites
at WCC recording similar concentrations (Fig.
5a). At all sites there is a coherent decrease
in concentration mid-way through the experimental
period. This can be related to a variation in
wind direction from SSW to SW which may have
switched the dominant wind direction at the
intersections from a mainly southerly to a
westerly flow. This would have temporarily
diverted the passage of the tracer away from the
Marylebone intersection and the majority of the
receptors.
Fig. 1. Site plan of the DAPPLE field site.
Westminster City Council (WCC), the base for the
field campaign, is on the SW corner of the
intersection. The sites were 17 fixed
instrument locations 3 tracer release positions
with up to 16 receptors and mobile personal
exposure and traffic flow measurements.
Fig. 7a.
CONCLUSIONS Despite the complexity of the urban
intersection topology the main features of the
mean wind field can be related to those described
in idealised 2-D canyons. This information can
be used to interpret in-street, time averaged,
tracer and pollution concentrations. Further
work is underway to relate these data to the
finer scale, real-time, non-static, personal
exposure measurements made during DAPPLE. For
more details and publications please see
http//www.dapple.org.uk
Fig. 7b.
Fig. 7a. Personal exposure monitoring across
Marylebone pavement. The Health and Safety
Laboratory visualisation equipment is in the pram
(centre). Fig. 7b. An example still of the
synchronised output from the video imagery and
Ptrak particulate data. This information is used
to relate exposure and person activity.