Isotopic characterisation of CO2 sources during regional pollution events using isotopic and radiocarbon analysis

At the station Kollumerwaard (The Netherlands), for monitoring tracers in the troposphere, air is sampled in 16 containers for off-line 13C, 18O and 14C isotopic analysis of CO2. The timing of the sampling is chosen such that CO2 variations correlating with pollutants like CO and CH4 are optimally covered. The 14C measurements enable us to discriminate between biospheric and fossil fuel contributions to atmospheric CO2. The analysis of one series sampled on 23 November 1994 resolves the increased CO2 mixing ratio into a purely biospheric component with a δ13C of (-22.2±1.5)‰, and a fossil component of up to 35 ppm with a δ13C of (-34.1±1.6)‰. Another series, recorded on 2 and 3 February 1995, shows a nearby emission of fossil CO2, methane and carbon monoxide, most likely due to the flaring of natural gas. Both events clearly indicate the importance of natural gas consumption in or in the vicinity of Holland. These experimental values can be compared with estimates of CO2 emissions from combustion of fossil fuels and the corresponding δ13C values. The results for 18O show the pronounced difference in behaviour between the O and C isotopes in atmospheric CO2, due to the fast isotopic exchange processes with (plant, soil or ocean) water. As a side result, the method produces the ratio CO: fossil CO2, a direct measure for combustion quality on a regional scale.