Relative measurements of ozone absorption cross‐sections at three wavelengths in the Hartley band using a well‐defined UV laser beam

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New measurements of absorption cross sections of ozone are reported using a photometer with a well‐defined UV laser beam at three different wavelengths in the Hartley band, by comparison with the conventional cross‐section value at the mercury line wavelength of 253.65 nm. Reported measurement results and uncertainties are dependent on the value of the cross section used at 253.65 nm. Using the value determined by Hearn (1961), ozone absorption cross‐section values of 9.64 × 10−18, 10.61 × 10−18, and 11.26 × 10−18 cm2 molecule−1 are reported at wavelengths of 244.06, 248.32, and 257.34 nm, respectively; whereas, use of the Malicet (1995) value leads to ozone absorption cross‐section values of 9.50 × 10−18, 10.45 × 10−18, and 11.12 × 10−18 cm2 molecule−1, respectively. In all cases, the uncertainty of the results is dominated by the contribution from the cross‐section value at 253.65 nm. The experimental setup described in this article not only provides a minor contribution to the entire reported measurement uncertainties but also confirms the internal consistency of previously published ozone absorption cross‐section data sets and demonstrates the biases that can be introduced by changing data sets. The results are important for the accurate measurement of ozone concentrations in the troposphere by UV absorption methods and also for all measurements of ozone concentration in the atmosphere by spectroscopic methods for which the values of the absorption cross sections have been scaled to measured values in the Hartley band.