CCQM-K120.a comparison involves preparing standards of carbon dioxide in air which are fit for purpose for the atmospheric monitoring community, with stringent requirements on matrix composition and measurement uncertainty of the CO2 mole fraction. This represents an analytical challenge and is therefore considered as a Track C comparison. The comparison will underpin CMC claims for CO2 in air for standards and calibrations services for the atmospheric monitoring community, matrix matched to real air, over the mole fraction range of 250 μmol/mol to 520 μmol/mol. CCQM-K120.b comparison tests core skills and competencies required in gravimetric preparation, analytical certification and purity analysis. It is considered as a Track A comparison. It will underpin CO2 in air and nitrogen claims in a mole fraction range starting at the smallest participant's reported expanded uncertainty and ending at 500 mmol/mol. Participants successful in this comparison may use their result in the flexible scheme and underpin claims for all core mixtures This study has involved a comparison at the BIPM of a suite of 44 gas standards prepared by each of the participating laboratories. Fourteen laboratories took part in both comparisons (CCQM-K120.a, CCQM-K120.b) and just one solely in the CCQM-K120.b comparison. The standards were sent to the BIPM where the comparison measurements were performed. Two measurement methods were used to compare the standards, to ensure no measurement method dependant bias: GC-FID and FTIR spectroscopic analysis corrected for isotopic variation in the CO2 gases, measured at the BIPM using absorption laser spectroscopy. Following the advice of the CCQM Gas Analysis Working Group, results from the FTIR method were used to calculate the key comparison reference values. KEY WORDS FOR SEARCH FTIR, CO2, GC-FID, Carbon dioxide at background level, Carbon dioxide at urban level, Delta Ray, CO2 gas standards Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

This key comparison aims to assess the core capabilities of the participants in gas analysis. Such competences include, among others, the capability of preparing Primary Standard gas Mixtures (PSMs), performing the necessary purity analysis on the materials used in the gas mixture preparation, the verification of the composition of newly prepared PSMs against existing ones, and the capability of calibrating the composition of a gas mixture. According to the Strategy for Key Comparisons of the Gas Analysis Working Group, this subsequent key comparison is classified as a track B key comparison, which means that the results of this key comparison can be used to underpin calibration and measurement capabilities for propane under the default scheme. The artefact was a binary mixture of propane in nitrogen at a nominal amount-of-substance fraction level of 1000 μmol/mol. The values and uncertainties from the gravimetric gas mixture preparation were used as key comparison reference values (KCRVs). Each transfer standard had its own KCRV. The result of the participating laboratory is consistent with the key comparison reference value within the respective expanded uncertainties and deviates less than 0.1 %. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

The dual-functionality sensor derived from semiconductor metal oxides operating at low temperature for low power consumption and robust stability toward humidity is a striking platform for economic and indoor air-quality monitoring. Therefore, in this work, temperature-dependent selectivity and robust stability toward carbon monoxide (CO), toluene (C7H8), and p-xylene (C8H10) are displayed by various TiO2 nanostructures synthesized following a facile hydrothermal method. The X-ray diffraction patterns confirmed the tetragonal structure of anatase TiO2. Surface studies confirmed the different morphologies, such as nanoparticles (TiO2 nanoparticles (TNPs)), nanowires (TiO2 nanowires (TNWs)), and sea-urchin-like hierarchically (HHC) arranged TiO2 nanostructures. Relatively high surface area and interconnected pore distribution were witnessed for TNWs and HHC nanostructures as compared to TNPs. In situ photoluminescence and X-ray photoelectron spectroscopy analyses confirmed the defect states of the nanostructures, and the TNWs possessed the highest concentration of oxygen vacancies and Ti3+, which influenced the dual-selectivity functionality of TNW toward C7H8 and C8H10 at 25 and 125 °C, respectively. Additionally, at an optimum working temperature of 25 °C, a response of 2.46 toward 20 ppm CO was witnessed for the HHC-based sensor and was attributed to the available surface area and active sites presented by the hierarchically arranged nanostructures. Cross-sensitivity measurements were conducted in the presence of interfering gases, which showed negligible cross-responses. The long-term stability in the presence of relative humidity and the sensing mechanism underlying the fascinating dual functionality for C7H8 and C8H10 vapor detection were discussed in detail. These findings showed that the current sensors can be employed for detection of C7H8 and C8H10 in a vastly robust and selective way with insignificant interference from ambient humidity.

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