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

o bs er vatio ns sh ou ld in clu de w hether the s tr eets are con g es ted o r qu iet an d th e p resen ce o f
any o th er diesel veh icles w ithin o ne block.
8. O ne r un in th e midd le of th e day w ill inclu d e sam plin g in th e f ro nt of th e bu s; th is will
r eq uire mo vin g th e D ataRAM an d the A ethalo m eter samp lin g tu b e to th e fo u rth ro w ,
d river’ s s id e ais le.
9. F or o ne 15 m inu te p eriod of r elatively stead y- state d riv in g con ditio ns , f ou r win do ws on each
s id e of th e b us s ho u ld b e o pened h alf- way ; th is perio d sh o uld be no ted in th e log b oo k.
10. Collect 10 m inu tes o f data on -s ite id ling af ter com pletion o f d aily samp lin g; d u ring id ling ,
the f ro n t do o r of th e bu s s ho uld r em ain o pen .
INSTRUMENT COMPARISON
To assure that both DataRAMs and both Aethalometers are comparable, these instruments
will need to be operated side-by-side for a period of at least 2 hours under a variety of air
conditions. All instruments will be loaded into a passenger car, connected according to the
protocol above and driven around in a variety of traffic conditions for a period of not less than
2 hours.
ANALYSIS
1. Download data from the DataRAMs and Aethalometer onto an IBM-compatible computer.
2. Perform time-adjustments to account for any differences in instrument clocks and sampling
hose length.
3. Compare data from instrument side-by-side comparisons, including graphs and timeweighted
averages; determine whether any correction factor is needed, and apply such
correction factor if necessary.
4. Observe data for any unexplained, isolated, low or high values; check data quality for those
points using Aethalometer diagnostics; discard data points only if they are single isolated
values more than two standard deviations above or below the mean, with no explanatory
factors recorded in the logbook at that time, and with questionable data quality.
5. Overlay the data from the two Aethalometers and from the two DataRAMs and graph them
on the same table; using the logbook, mark events during high and low periods.
6. Calculate time-weighted averages for in-car and in-bus data; compare these averages.
7. Using the logbook and map, designate portions of the route “uphill,” “downhill,” “flat” and
calculate time-weighted averages for these different conditions in the bus and car.
8. Using the logbook, designate portions of the route “idling,” “stop-and-go,” and “steady
driving” and calculate time-weighted averages for these conditions in the bus and car.
9. Subtract the overall time-weighted average of black carbon calculated on the car from that
calculated on the bus; apply appropriate correction factors 131 to convert black carbon to
elemental carbon, and to convert elemental carbon to diesel exhaust particulate; 132 compare
with Cal EPA significant risk number adjusted for school bus scenario (see attached risk
assessment) to calculate excess cancer risk to a child attributable to riding that school bus.
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