DEVELOPING STATIC AND DYNAMIC STABLE ISOTOPE REFERENCE GAS MIXTURES OF CO2 AT 400 µmol/mol

Climate change is one of the most urgent issues facing humanity today. Humans have been rapidly changing the balance of gases in the atmosphere which causes global warming. Burning fossil fuels like coal and oil, farming and forestry, agriculture and cement manufacture cause to release water vapor, carbon dioxide (CO₂), methane (CH₄), ozone and nitrous oxide (N₂O) known as the primary greenhouse gases. According to Intergovernmental Panel on Climate Change (IPCC), carbon dioxide is the most common greenhouse gas absorbing infrared energy emitted from the earth, preventing it from returning to space. It is necessary to separate man-made (anthropogenic) emissions from natural contributions in the atmosphere to obtain accurate emission data [1-4]. Since it could not be achieved with the existing metrological infrastructure, it is required to develop the measurements and references of stable isotopes of CO₂. In this study, static and dynamic reference materials for pure CO₂ at 400 µmol/mol in air matrix were prepared and it was provided to simulate CO₂ gas in the atmosphere.

The static gas mixtures were prepared gravimetrically in accordance with the ISO 6142-1 standard. In order to obtain CO₂ gas at desired isotopic compositions, commercial CO₂ gases were also supplied from abroad. Their isotopic compositions were measured by using GC-IRMS. Before filling, aluminum cylinders were evacuated until the pressure of 10^-7 mbar using turbo-molecular vacuum pump. Isotopic compositions of reference materials were determined in a way that covering the range -42 ‰ to +1 ‰ vs VPDB for d¹³C-CO2 and -35 ‰ to -8 ‰ vs VPDB for d¹⁸O. In order to develop static and dynamic reference materials of CO₂ at 400 µmol/mol in air with the uncertainty targets of d¹³C-CO₂ 0.1 ‰ and d¹⁸O-CO₂ 0.5 ‰, previously prepared pure CO₂ reference gases were used. Dynamic dilution system with the high accuracy was constructed to generate dynamic reference gas mixture of CO₂ at 400 µmol/mol. System contains 3 electronic pressure controllers, 3 thermal mass flow controllers with various capacities and 3 molbloc-L flow elements commanded with 2 Molboxes. The isotopic compositions of dynamic reference gas mixtures of CO₂ at 400 µmol/mol were aimed to be same with the previously prepared pure CO₂ reference gases. The whole dilution system were calibrated at INRIM to achieve lower uncertainties around 0.07-0.09%. At the measurement stage, CRDS and GC-IRMS equipments are operated simultaneously to determine the concentrations and isotopic compositions of the gas mixtures. The amount of substance fractions of the dynamic reference mixtures are calculated according to ISO 6145-7 standard. It will be checked that whether the isotopic compositions of the gravimetrically prepared pure CO₂ reference gases and the dynamic reference gas mixtures of CO₂ at 400 µmol/mol were same or not.

REFERENCES

[1] Calabro P. S., “Greenhouse gases emission from municipal waste management: The role of separate collection”, Waste Management, Volume 29:7, 2178-2187, 2009.

[2] Sources of Greenhouse Gas Emissions, United States Environmental Protection Agency, https://www.epa.gov/ghgemissions/sources-greenhouse-gas-emissions, 2019.

[3] Schwartz, S.E., “The Greenhouse Effect and Climate Change”, 2017.

[4] Climate Change, The Intergovernmental Panel on Climate Change, https://www.ipcc.ch/report/ar4/wg1, 2019.