Final report on Pilot Study CCQM-P110: Study on the accuracy and uncertainty of FT-IR methods calibrated with synthetic spectra for NO2 concentration measurements

Abstract

The results of the first pilot study designed to evaluate the level of comparability of measurements of nitrogen dioxide (NO2) mole fractions in nitrogen based on measurement procedures that rely on FT-IR spectroscopy as an absolute method of quantification with the traceability of measurement results to line strength data are reported.Participants were required to report measurement results using FT-IR for the gas standard (nominal mole fraction of 10 µmol/mol NO2 in nitrogen) received from the BIPM as part of the CCQM-K74 exercise. In addition, they were required to provide infrared spectra and instrument parameter information to enable a recalculation of their results by the BIPM's, using only its own synthetic spectra calibration procedure with values traceable to the line parameters contained in HITRAN 2004.The relative standard uncertainties based on FT-IR measurements reported by participating laboratories ranged from 0.6% to 4.3%. The relative standard uncertainty of the reference value for each gas standard was 0.4%, as determined during the CCQM-K74 exercise. Of the ten results submitted, only five agreed with the reference value within their expanded uncertainties. Furthermore, major contributions to the uncertainty of FT-IR measurements arose from the optical path length measurements and the uncertainty that could be attributed to line strength data from the HITRAN molecular database. The inclusion of these uncertainty contributions was estimated by the BIPM to result in achievable relative standard uncertainties of 3.4% for its FT-IR measurements using synthetic spectra calibration procedures.Finally the recalculation of the participants' results by the BIPM using the laboratories' submitted experimental characteristics and infrared spectra showed good agreement with the submitted results, indicating that the calculation algorithms were not in themselves a major reason for the spread of results.Main text.To reach the main text of this paper, click on Final Report.The final report has been peer-reviewed and approved for publication by the CCQM-GAWG.