An updated estimation of the stable carbon and oxygen isotopic compositions of automobile CO emissions

摘要

We estimate up-to-date values of the average isotopic compositions of CO emitted from automobiles. In the estimation, we determined the isotopic compositions of CO in tail pipe exhaust for four gasoline automobiles and two diesel automobiles under varying conditions of both idling and running. While the dependence on the automobile manufacturer is little, each automobile equipped with functional catalytic converter exhibits a large temporal δ~(13)C and δ~(18)O variation. They tend to show ~(13)C and ~(18)O enrichment in accordance with the reduction of CO in exhaust, suggesting that the functional catalytic converter in engines enhances the δ~(13)C and δ~(18)O values of CO from tail pipes through a kinetic isotope effect during CO destruction. Assuming that automobiles run a modeled driving cycle, we estimated the average δ~(13)C and δ~(18)O of CO to be -23.8+-0.8 per thousand_(PDB) and +25.3+-1.0 per thousand_(SMOW), respectively, for recent gasoline automobiles, and -19.5 +- 0.7 per thousand_(PDB) and + 15.1 +- 1.0per thousand_(SMOW), respectively, for recent diesel automobiles. While the δ~(13)C and δ~(18)O values of recent gasoline automobiles coincide well with the isotopic compositions of source CO in present trunk road atmosphere estimated in this study, those are +4- + 6 per thousand (δ~(13)C) and + l-+3per thousand (δ~(18)O) higher than those reported previously and also those emitted from old, non-catalyst automobiles determined in this study. Recent improvemems in functional catalytic converters have enhanced and will enhance the δ~(13)C and δ~(18)O values of CO from automobiles.