NRDC: No Breathing in the Aisles: Diesel Exhaust Inside School ...

would face an additional cancer risk of between 1.7 and 3.3 potential excess cancers per
million children so exposed. If the levels of diesel exhaust particulate on the bus exceed 1
mcg/m 3 , then the risk would be proportionately greater, whereas if the levels are lower, the
risk would be less.
Calculation of Excess Risk Attributable to School Buses Based on Monitoring
Data
Crown 1986(b) - 6.7 mcg/m 3 above ambient level of diesel exhaust (black carbon)
Conversion factor from black carbon measured by Aethalometer to elemental carbon = 1.32 136
Conversion factor from elemental carbon to diesel exhaust particulate = 1.56 137
1 hour per day
(6.7 mcg/m 3 ) x (1.32) x (1.56) x (1.7 x 10 –6 ) = 23 x 10 –6
2 hours per day
(6.7 mcg/m 3 ) x (1.32) x (1.56) x (3.3 x 10 –6 ) = 46 x 10 –6
Explanation of Calculation of Excess Risk Attributable to School Bus
A child riding a school bus with the highest average black carbon values we found would face
an excess risk of 23–46 potential cancers per million children so exposed. This risk assumes
that child is riding the bus every school day for 10 years.
46