CO, NO x and 13CO 2 as tracers for fossil fuel CO 2: results from a pilot study in Paris during winter 2010
Measurements of the mole fraction of the CO 2 and its isotopes were performed in Paris during the MEGAPOLI winter campaign (January–February 2010). Radiocarbon ( 14CO 2) measurements were used to identify the relative contributions of 77% CO 2 from fossil fuel consumption (CO 2ff from liquid and gas combustion) and 23% from biospheric CO 2 (CO 2 from the use of biofuels and from human and plant respiration: CO 2bio). These percentages correspond to average mole fractions of 26.4 ppm and 8.2 ppm for CO 2ff and CO 2bio, respectively. The 13CO 2 analysis indicated that gas and liquid fuel contributed 70% and 30%, respectively, of the CO 2 emission from fossil fuel use. Continuous measurements of CO and NO x and the ratios CO/CO 2ff and NO x/CO 2ff derived from radiocarbon measurements during four days make it possible to estimate the fossil fuel CO 2 contribution over the entire campaign. The ratios CO/CO 2ff and NO x/CO 2ff are functions of air mass origin and exhibited daily ranges of 7.9 to 14.5 ppb ppm −1 and 1.1 to 4.3 ppb ppm −1, respectively. These ratios are consistent with different emission inventories given the uncertainties of the different approaches. By using both tracers to derive the fossil fuel CO 2, we observed similar diurnal cycles with two maxima during rush hour traffic.