We have found that measurements of environmentally relevant parameters generate some of the greatest student enthusiasm in our freshmen chemistry laboratories. In this regard we have developed a lab exercise to investigate and compare the carbon monoxide content of automobile exhaust and cigarette smoke using equipment available in most undergraduate labs. This experiment uses gas chromatography with thermal conductivity detection to analyze for the % by volume concentrations typically found in cigarette smoke and auto exhaust. Students are usually surprised to discover that cigarette smoke has a much higher CO concentration than does the exhaust from a clean, well maintained vehicle.