Measuring Carbon Monoxide in Auto Exhaust by Gas Chromatography Dan Jaffe and Scott Herndon University of Alaska Fairbanks, Fairbanks, AK 99775 Carbon monoxide is an odorless, colorless gas that is toxic a t concentrations greater than 0.1% viv (1000 parts per million by volume (ppmv1 (11. (Air pollutants are commonly reported as a volumetric 'tnixing ratio" which is identical to a mole fraction.) At lower concentrations CO causes health problems by binding to hemoglobin in the blood stream, reducing its ability to transport oxygen. Cars are the major source of CO to the atmosphere in urban areas. They emit exhaust containing anywhere from near 0 to 15% CO (vlv). Primarily due to automotive emissions, many cities frequently violate the CO air quality standard (9 ppm viv for an 8-h average). This omblem is not confined to large cities. Fairbanks, Alaska ipopulation -50,0001 routine1;violates the CO standard several times each winter. althowh the frequency of violations has diminished in recent years. CO violations are more common during winter possibly due to several factors. Atmospheric inversions, which reduces dispersion and dilution of pollutants, are more common during winter. Another possible contributor is increased combustion during winter due to increased driving and combustion of fuels for heating. A third possible cause is that cars are known to emit G a t e r CO eoncentrations when started a t cold temoeratures. Determining the importance of each of the factors listed above i s necessary to take effective action. Many cities require annual testing of registered vehicles for CO and hydrocarbon emissions via "Inspection and Maintenance (IMY proerams. Vehicles that do not meet some minimum standard must be repaired or receive a waiver. Recently, concerns have been raised that state IM programs do not significantly improve air quality (2). Based on tests of on-road vehicles. these authors believe that a large fraction of the CO emisiions are due to a small percentage of the vehicles (2). For air qnalitv monitoring, - CO concentrations are most commonly determined using a non-dispersive infrared (NDIR) instrument (3).Several manufacturers sell instrumentation for automotive exhaust andlor ambient concentrations of CO. However, these are not available routinely in undergraduate chemistry labs. Our goal in this work was to develop a simple and reliable technique using commonly available equipment to make environmentally relevant measurements i n our undergraduate chemistry labs. A gas chromatograph with thermal condnctivitv detector (TED)is used fo;this work. In various forms, wehave used this experiment with excellent results in classes ranging from honors first-year chemistry to senior instrumental analysis labs. Normally two three-hour lab periods are sufficient. There are several important benefits realized from developing environmentally relevant projects for nndergraduate labs. First, students come to realize that science is not about finding the "right" answer (the answer that the teacher believes to be correct). The students also enjoy solving a real-world problem using their chemical skills and knowledge. Lastly, students are especially "turned on" by working on environmental problems involving cars. 364
Journal of Chemical Education
Experimental The materials consist of plastic zipper-type sample bags (1 pint size) to collect auto exhaust, a 6 ft x l/4 in. 0.d. stainless steel column packed with 5Amolecular sieves, dry He carrier gas, the W-TCD, chart recorder or computerized data acaui&ion system, and a l-mLgas tight ~ y r & ~ Our e . experiments use a Gow/Mac series 150 gas chromatograph with a thermal conductivity detector. The detector current is set to 190 mA. The molecular sieve column was activated for 30 h with He flowing, but disconnected from the detector. The column was reactivated aRer two lab periods of use. CO determinations are made a t 5 0 6 0 OC with a carrier flow rate of 60 mWmin. 'Chc at;inderd i s ;I cornrnwri:rlly nvnilahlr lecture bottle
