Measurements of stable carbon and oxygen isotopic compositions of CO in automobile exhausts and ambient air from semi-urban Mainz, Germany

Stable isotopic measurements of atmospheric CO ((CO)-C-13, (CO)-O-18) were carried out at three season in a middle size city, Mainz in Germany. CO sta ble isotopic compositions of car exhaust fueled by gasoline, diesel and nat ural gas were also measured and showed different isotopic compositions (del ta(18)O vs. V-SMOW = 22.3 +/- 0.3 parts per thousand, 10.9 +/- 0.8 parts pe r thousand, 20.1 +/- 1.0 parts per thousand and delta(13)C vs. V-PDB = -29. 9 +/- 0.3 parts per thousand, -22.2 +/- 1.1 parts per thousand, -51.3 +/- 1 .5 parts per thousand, respectively). The O-18/O-16 ratios of atmospheric C O in Mainz show a clear linear correlation with the reciprocal concentratio n of CO. This reveals the contribution of CO emitted from a single pollutio n source (delta(18)O = 20.7 +/- 0.5 parts per thousand V-SMOW), whose isoto pic composition is close to that of CO from a gasoline engine combustion. F rom this value and car exhaust measurements, about 14 +/- 7% of CO in Mainz air is estimated to originate from diesel fuel engine combustion. The oxyg en isotopic composition can be used as a good indicator of contamination fr om car exhausts. On the other hand, the C-13/C-12 ratios of CO do not show a clear relationship with the reciprocal concentration of CO.