Passage II

Carbon monoxide gas (CO) is toxic in air at concentrations above 0.1% by volume. Cars are the major source of atmospheric CO in urban areas. Higher CO levels are observed during colder weather. A group of students proposed that cars emit more CO at colder air temperatures than at warmer air temperatures during the first 15 minutes after they are started. The students did the following experiments to investigate this hypothesis.

Experiment 1

A hose was connected to the tailpipe of a car. The engine was started and the exhaust was collected in a plastic bag. A 1 mL sample of the exhaust was taken from the bag with a syringe and injected into a gas chromatograph, an instrument that separates a mixture of gases into its individual components. Comparisons of the exhaust with mixtures of known CO concentrations were made to determine the percent by volume of CO in the exhaust. Exhaust was collected at 2-minute intervals. Samples of exhaust from each of 4 cars were tested at an external temperature of -9°C. The results are shown in Table 1.

Experiment 2

The same 4 cars were tested at a temperature of 20°C using the procedure from Experiment 1. The results are shown in Table 2.