NPL: Institute of Physics medal for Paul Brewer for the new global reference value of the ozone absorption cross-section — according to NPL about 1.2% lower than the previous standard and six times more accurate
On 12 October 2026 the UK’s National Physical Laboratory (NPL) announced that Paul Brewer has been awarded the 2026 Institute of Physics (IOP) Edward Appleton Medal for his contributions to atmospheric science and his leadership in improving the accuracy of ozone measurements used around the world.
- The award concerns the ozone absorption cross-section — a fundamental parameter used to measure atmospheric ozone and underpinning air-quality assessments worldwide. According to NPL, Brewer led a five-year international task group which, through a review of more than 60 years of research supported by new independent laboratory measurements, established a new global reference value.
- The new value, identified as CCQM.O3.2019, refers to absorption at 253.65 nm (in air). According to the International Bureau of Weights and Measures (BIPM) it is just over 1% lower than the previous Hearn 1961 value, with the relative uncertainty reduced to 0.31%; NPL gives a difference of about 1.2% and a sixfold improvement in accuracy.
- Among updated documents the BIPM listed US EPA regulations (Code of Federal Regulations Part 50, Appendix D) and two ASTM standards, and among those under revision, among others, ISO 13964 and EN 14625 (ozone measurement by UV photometry). According to the BIPM (2024), instruments and networks were to switch to the new value from 1 January 2025 with a one-year transition period; NPL states that the value has now been implemented across global monitoring networks and incorporated into legislation.
- The BIPM recommended that ozone measurement results indicate — by flagging data or in the metadata — which cross-section value was used, and announced that from 1 January 2025 the new value would also apply in the international comparison of ozone standard reference photometers, BIPM.QM-K1. The CCQM-GAWG task group has also published guidance on units and rounding of the value for documentary standards and on implementing the new cross-section in ozone concentration measurements.