Passage III

Motor vehicle exhaust is a significant source of several air pollutants, including the nitrogen oxides, NO₂ and NO. Scientists performed two experiments to investigate the levels and behavior of these pollutants and naturally occurring gases in the atmosphere near busy roadways.

Experiment 1

Scientists studied how NO₂, levels vary with vehicle use. They measured NO₂ levels hourly for a 24-hour period, 10 meters (m) downwind from six roadways. Each roadway had a combination of a different speed limit and vehicle usage (approximate number of vehicles per day). An average NO₂ value for each roadway was calculated in parts per billion (ppb). The results are in Table 1.

Experiment 2

Next, levels of NO₂ and NO were measured at 0, and 100 m downwind from the 100 km/hr roadway which averaged 30,000 vehicles per day. The level of NO₂ decreased from 30 ppb at 0 m to 17 ppb at 100 m. The level of NO decreased from 150 ppb at 0 m to 42 ppb at 100 m.

(Note: The levels of NO₂ and NO that would be found far from pollution sources are 15 ppb and 35 ppb, respectively.)

Experiment 3

Ozone (O₃) is a naturally occurring gas in the atmosphere. Levels of ozone, in parts per million (ppm) were taken at various distances downwind from the 100 km/hr roadway which averaged 30,000 vehicles per day. The results are in Table 2.

(Note:The naturally occurring ozone concentration is 0.12 ppm.)