2.2. Sampling strategy
Diffusive BTX samplers (Perkin Elmer) were exposed
to ambient air for 28 consecutive 7-day periods betweenJune and December 2001. The samplers were placed at
2.6 m height at the 10 roadside locations indicated with
capital letters in Fig. 1, and at one urban BG site in
Montsouris Park. In addition, diffusive samplers were
exposed at different heights (2nd, 5th and 10th floor)
near the walls of the asymmetric canyon in Av. Leclerc
during1 week (16–23 July 2001). Duringthe same week,
a mobile monitoringunit (trailer) was parked on the east
side of the canyon, inside the separate parkinglane.
That allowed recordingof hourly CO, NOx and O3
values continuously duringday and nighttime. Furthermore,
active VOC samplingwas conducted at the same
location by drawingambient air during12 one-hour
intervals at a constant flow through Supelco tubes.
Hourly CO and NOx values for the year 2001 were
also obtained from the air quality monitoringstation
(AIRPARIF) permanently operatingin Pl. Basch. Theexact location of this station is on a narrow traffic island
in the middle of a pedestrian crossingat the intersection
of Av. Leclerc with Pl. Basch (Fig. 1). Synoptic
meteorological data were obtained from weather stations
in Montsouris Park and Orly Airport throughout
the campaign. During the intensive monitoring period
(16–23 July), two anemometers (a 3D ultrasonic and a
mechanical microvane) and a weather mini-station
equipped with temperature, humidity and global radiation
sensors were located next to the mobile unit on the
east side of Av. Leclerc, at 4.8 m height above the
ground and 10.3 m distance from the nearest building
wall. Hourly traffic volumes and average vehicle speeds
were obtained from automatic counters operated by the
local authority of Paris (Mairie de Paris) within the
selected road segment. Manual vehicle counts were
taken duringthe campaign and compared for consistency with the data obtained from the automatic
network. The vehicle fleet composition (i.e. percentage
of heavy duty vehicles, light duty vehicles, buses,
motorcycles, and passenger cars) was determined from
on-site observations. Furthermore, national statistics
were used to estimate the vehicle fuel type. Finally, a
QA/QC programme including sampling duplicates, field
and laboratory blanks, and instrument calibration with
standard gases was followed throughout the campaign.