FTIR-based spectral line data of the v3 band of NO2 at 6.3 µm and multi-component impurity analysis of NO2 reference gases within the scope of the EMPIR MetNO2 project

Air pollution causes hundreds of thousands of premature deaths every year in Europe [1]. Traffic related Nitrogen dioxide (NO₂) is a key contributor whose concentration is legislated by the Ambient Air Quality Directive (EU, 2008) [2] and the air quality guidelines (AQGs) set by the World Health Organization (WHO). Atmospheric NO₂ concentration has been widely measured by national, regional and global monitoring networks using different instrumentations. SI-traceability is essential to assure data comparability across networks, underpinning long term trend of ambient NO₂.

Traceable and accurate spectral line data [3,4] of NO₂ is essential for optical sensing of NO₂ using in situ [5] and satellite-based equipment. In particular, it is essential for cost-effective light-weight systems with payload restrictions (e.g. TDLAS system [6], e.g. when installed on drones and balloons for which real time calibration using gas cylinders quickly becomes a burden). Within the scope of the EMPIR (The European Metrology Programme for Innovation and Research) MetNO₂ project [7], spectroscopic measurements of the selected NO₂ CRM (certified reference material) has been carried out using the FTIR infrastructure at PTB to a) derive traceable line data of NO₂; b) quantify the amount of impurities, such as HNO₃, N₂O₄, NO, N₂O, CO, H₂O, etc. Here, we report the line intensity and air-broadening coefficients of the 6.3µm v₃ band of NO₂. FTIR-based impurity analysis including their temporal evolution will also be presented.

Acknowledgement

MK and GL thank for technical support from Kai-Oliver Krauss. This work has received funding from the EMPIR programme co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation programme. PTB is member of the European Metrology Network for Climate and Ocean Observation (https://www.euramet.org/european-metrology-networks/climate-and-ocean-observation/).

References

[1] Air quality Europe – 2019 report.  EEA Report No 10/2019. https://www.eea.europa.eu/publications/air-quality-in-europe-2019

[2] Directive 2008/50/EC of the European Parliament and of the Council of 21 May 2008 on ambient air quality and cleaner air for Europe. https://www.eea.europa.eu/policy-documents/directive-2008-50-ec-of

[3] V. Werwein, J. Brunzendorf, G. Li, A. Serdyukov, O. Werhahn, V. Ebert.  Applied Optics 56 (2017)

[4] V. Werwein, G. Li, J. Brunzendorf, A. Serdyukov, O.Werhahn, V. Ebert. Journal of Molecular Spectroscopy 348, 68-78(2017).

[5] O. Werhahn O, J.C. Petersen (eds.) 2010 TILSAM technical protocol V1_2010-09-29. Available from:                     http://www.euramet.org/fileadmin/docs/projects/934_METCHEM_Interim_Report.pdf.”

[6] J. A. Nwaboh, Z. Qu, O. Werhahn and V. Ebert, Applied Optics 56, E84-E93 (2017)

[7] EMPIR project 16ENV02, “Metrology for Nitrogen Dioxide (MetNO₂)”, http://em-pir.npl.co.uk/metno2/