Exposure of Cyclists to Ultra Fine Particles - Highway and Urban Environment - page 110

PM10 (µg/m 3 )
UFP (particles/cm 3 )

140000

Busy Traffic on N18

120000

90

Construction site 1 Construction site 2

100000

80

70 80000

60 60000

50 40000

40 20000

30 0

7:29 7:31 7:34 7:37 7:40 7:43 7:46

Time (CET)

Fig. 3 Patterns of PM10 and UFP are related to different sources

500 7

450 6

P1
P2
Ratio
P1/P2

Direction
South

400 5

North North

South North South

350 4

300 3

250 2

200 1

150 0

100 -1

50 -2

0 -3

7:40:48 :55:12 8:09:36 :24:00 8:38:24 :52:48 9:07:12 :21:36

Time (CET)

Fig. 4 Number of particles on the cycling track (P1 closest to the road, P2 1 m further away from
the road). Six trips on April 2, 2008

(~4%) between both instruments. It was therefore decided to repeat the test with
N = 10 which should allow us to determine the significance of the difference at the
p = 0.01 level.
The preliminary results were confirmed in the second test although average
particle numbers (~20,000 cm −3 ) were significantly lower than during the pilot test
( t -test p < 0.001). Some results are shown in Fig. 4 .