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Des mesures plus exactes de l’ozone troposphérique : bientôt une réalité !

Preparations for the implementation of a new ozone cross section value worldwide allowing more accurate measurements of surface ozone are going to plan. The new value (CCQM.O3.2019 value) is just over 1 % lower than the current value (Hearn.1961 value) with a relative uncertainty that is reduced to 0.31%. Five key technical normative documents have been revised and published to include the new value, with a remaining three to be published in the next months. The efforts to achieve a coordinated update of normative standards has been led by the CCQM-GAWG Task Group on Ozone Cross-Section Change Management, which has also published guidelines on:

Regulations/written standards that have recently been updated are:

  • US EPA Code of Federal Regulations Part 50 Appendix D - Reference Measurement Principle and Calibration Procedure for the Measurement of Ozone in the Atmosphere (Chemiluminescence Method)
  • Japanese Standard JIS B 7957:2006/AMENDMENT 1:2023 Continuous analyzers for ozone and oxidants in ambient air (Amendment 1)
  • Australian Standard AS 3580.6.1 (2023), Methods for sampling and analysis of ambient air, Method 6.1: Determination of ozone - Direct-reading instrumental method
  • ASTM Standard D5110-98 (2022), Standard Practice for Calibration of Ozone Monitors and Certification of Ozone Transfer Standards Using Ultraviolet Photometry
  • ASTM Standard D5110-02 (2022), Standard Test Methods for Continuous Measurement of Ozone in Ambient, Workplace, and Indoor Atmospheres (Ultraviolet Absorption)

Standards that are currently under revision with updates to be published in 2024 are:

  • International Standard ISO 13964 (1998), Air quality - Determination of ozone in ambient air - Ultraviolet photometric method
  • International Standard ISO 10313 (1993), Ambient air - Determination of the mass concentration of ozone - Chemiluminescence method
  • European Standard EN 14625 (2012), Ambient air - Standard method for the measurement of the concentration of ozone by ultraviolet photometry

Further information is available at

Implementation of the new absorption cross section in surface ozone measurements instruments and networks is expected to start on 1 January 2025 with a transition period of 1 year, with all systems expected to be using the new cross section value by 1 January 2026. The CCQM-GAWG Task Group has recommended that those making surface ozone measurements should ensure that before 1 January 2025 they are able to indicate which ozone cross section is being used either by flagging data or including the information in the metadata they provide.

The absorption cross section used for the international comparison of ozone standard reference photometers (BIPM.QM-K1) will also be changed to the new value on 1 January 2025.