Car exhaust contains gases and particles that can reach freshwater habitats far from the road. Hydra — small organisms that live in ponds and respond quickly to changes in water quality — make useful living pollution detectors. You place groups of hydra in two sealed environmental chambers: one receives automobile exhaust delivered through a tire inner tube, the other holds normal room air as a control. Every 24 hours you examine both groups under a stereo microscope and record changes in body shape, feeding behavior, and survival. Over several days the differences between the exhaust-exposed group and the control reveal whether small doses of car exhaust can harm freshwater life.

Carbon monoxide is one of the gases that comes out of a car's exhaust pipe. Older vehicles tend to release more of this harmful gas than newer ones. A 20-year-old car produced the highest carbon monoxide readings, while a new car of the same make and model produced the lowest.

Bumper-to-bumper traffic may release worse air pollution than free-flowing traffic at the same location. To test this, you position a video camera above a 200-meter stretch of highway with a 90 km/h speed limit and record 18 hours of traffic from 6 a.m. to midnight. The footage splits into six 3-hour windows, and for each you measure average vehicle speed, traffic volume, and flow pattern. Peak commute hours — early morning and late evening — produce the highest pollution scores, consistent with the hypothesis that exhaust emissions are most severe during rush hour.

Exhaust pollutants travel through the air and settle on nearby vegetation. Pine trees next to busy roads show the effect in a measurable way: their needles develop fewer stomata, the tiny breathing pores that control gas exchange. You collect needle samples from 15 pine trees across three locations with different traffic concentrations. Back in the lab, you press a clear nail polish impression from each needle onto a glass slide and count the stomata under a microscope. Trees near high-traffic roads consistently show lower stomata density than those in quieter areas.

Stop-and-go driving during rush hour burns fuel less efficiently, pushing more gases and particles out of the exhaust pipe. One experiment captures this directly: a video camera records an 18-hour stretch of highway traffic, splitting the footage into six 3-hour windows. For each window, you estimate average speed, count vehicles, and note the flow pattern. Those factors combine into a pollution index that makes it possible to compare emission levels across the day.