Table 2 Percent contribution of bus commute to daily UFP and BC for a range of ambient levels.

From: Personal exposures to traffic-related air pollution in three Canadian bus transit systems: the Urban Transportation Exposure Study

Pollutant City Mean daily concentration (SD) Mean % contribution by ambient condition (SD)a
Riding Waiting Low Moderate High
Ultrafine Toronto 16.2 (4.1) 24.5 (7.5) 14.7 (3.3) 8.0 (1.9) 5.5 (1.3)
particles Ottawa 18.9 (8.5) 26.9 (15.5) 16.2 (6.4) 8.9 (3.9) 6.2 (2.8)
(103 pts/cm3) Vancouver 16.1 (12.1) 18.4 (14.2) 13.0 (8.6) 7.1 (5.0) 4.9 (3.5)
Black Toronto 3.1 (2.0) 4.6 (4.3) 23.0 (11.9) 13.5 (8.0) 9.6 (6.0)
Carbon Ottawa 2.6 (1.4) 2.8 (1.5) 19.4 (9.0) 11.0 (5.5) 7.7 (4.0)
(µg/m3) Vancouver 2.6 (0.6) 2.0 (0.6) 19.1 (3.5) 10.6 (2.1) 7.3 (1.5)
  1. Calculated for each daily mean waiting and riding (n = 30). Low ambient: 5 × 103 pts/cm3 UFP and 0.5 µg/m3 BC; moderate ambient: 10 × 103 pts/cm3 UFP and 1.0 µg/m3 BC; high ambient: 15 × 103 pts/cm3 UFP and 1.5 µg/m3 BC.
  2. aPercent contribution of 66-min bus commute (4.6% of day) to overall daily exposure (Eq. 2).