Two of the most commonly used solid biomass sources for fuel are wood chips and wood pellets. The calorific value and the moisture content of those biofuels determine the efficiency of the CHP and the biorefinery plants. Therefore, with the increased shift towards a biobased economy, the biomass cost and its physical properties must be precisely determined. Most of the current standards are lacking and provide neither enough details about the issues caused by the biomass heterogeneity nor with the variation in experimental practice. Phenomena such as data scattering, poor repeatability and wide uncertainty, are mostly observed during the measurements of the calorific value and the moisture content. To overcome such issues, an interlaboratory comparison between three national metrology institutes using bomb calorimetry has taken place. The comparison helped to identify the root causes behind the poor reproducibility of the wood samples. Factors such as the equilibrium moisture content of the biomass, the pellet mass, the applied pressure to form the pellet, the handling techniques and the determination errors are highlighted and analyzed. The final results paved the way to provide an enhanced detailed experimental practice where the repeatability and reproducibility have been strongly improved. Moreover, the detailed uncertainty sources and calculations are presented. It has been found that by fulfilling the recommended approach the measurement repeatability improved by up to 50–80%, while the final uncertainty improved by 10–30%. This enhancement leads to a maximum relative expanded uncertainty of around ±1% (coverage factor of k = 2 and a confidence level of 95%).

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.