ciddor_1996 =========== P\. E\. Ciddor, "Refractive index of air\: new equations for the visible and near infrared", Appl\. Opt\. 35, 1566 \(1996\) `Source record `__ · :doc:`Catalogue ` · :doc:`Review register ` DOI: `10\.1364/ao\.35\.001566 `__ **Source kind:** compilation **Recorded technique:** Equations for the phase and group refractivity of moist air\: the standard dry air's dispersion \(Peck and Reeder's, amended to ITS\-90 and to 450 ppm CO2\), a CO2 correction, water vapour's \(Erickson's, scaled by 1\.022\), and the BIPM 1981/91 density equation, combined through Lorentz\-Lorenz; compared with Birch and Downs's measurements at 633 nm \(1 part in 1e8\) and Peck and Reeder's over 230\-1690 nm\. No new measurements\. **Materials in structured entries:** dry air **Dataset quantities:** None recorded. **Contents:** 0 datasets; 1 formula. Curation notes -------------- Identity VALIDATED\_WITH\_WARNINGS by the library\. Printed pp\. 1566\-1573\. THE STANDARD DRY AIR \(p\. 1567, Eqs\. 1\-2, the constants from Appendix A, p\. 1571, checked against the page image\)\: standard air is dry air at 15 C, 101325 Pa and 450 ppm CO2, and 10^8 \(n\_as \- 1\) = k1/\(k0 \- sigma^2\) \+ k3/\(k2 \- sigma^2\), sigma the vacuum wavenumber in um^\-1, with k0 = 238\.0185, k1 = 5792105, k2 = 57\.362, k3 = 167917 um^\-2\. For x\_c ppm of CO2, \(n\_axs \- 1\) = \(n\_as \- 1\) \[1 \+ 0\.534e\-6 \(x\_c \- 450\)\] \(Eq\. 2\), Birch and Downs's factor at 633 nm\. Peck and Reeder's data span 230\-1690 nm; the equations 'should apply over the wavelength range from approximately 300 nm to 1690 nm' \(p\. 1571\)\. Uncertainty \(pp\. 1566, 1568\)\: refractometers disagree by 1\-3e\-8 \(1 sigma\) on one sample; 'one cannot expect an overall uncertainty of better than 2\-5 x 10^\-8' in n, with the BIPM density contributing 1\.4\-3\.5e\-8\. The dispersion equations of Edlen and of Peck and Reeder differ by below 0\.5e\-8\. The formula is recorded, not built into a model\: its medium is air, which is not a curated species\. OEP 1's air model is compared with it \(TC\-759\)\. **Recorded bibliographic identity status:** VALIDATED\_WITH\_WARNINGS. This concerns identification of the source; it does not establish the scientific correctness of its contents. Datasets -------- No datasets are recorded. Formulas -------- ciddor\_1996/standard\_dry\_air ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "standard_dry_air", "material": "dry air", "equation": "Eqs. (1)-(2), p. 1567; constants Appendix A, p. 1571", "printed": "10^8 (n_as - 1) = k1/(k0 - sigma^2) + k3/(k2 - sigma^2); (n_axs - 1) = (n_as - 1)[1 + 0.534e-6 (x_c - 450)]", "variable": "sigma = 1/lambda, lambda the vacuum wavelength in micrometres; x_c the CO2 content, ppm", "state": "15 C, 101325 Pa, dry, 450 ppm CO2", "density": "real", "range": "about 300-1690 nm (p. 1571)", "coefficients": { "k0": "238.0185", "k1": "5792105", "k2": "57.362", "k3": "167917", "co2": "0.534e-6" }, "check": "The constants read from the page image of Appendix A (p. 1571), 2026-09-30. At 633 nm Eq. (1) gives 10^8 (n_as - 1) = 27653.0 for standard dry air. Table 1 compares moist air at laboratory states, through the full procedure (water vapour, BIPM density), which is not reproduced here." } Corrections ----------- No dataset errata are recorded in this source record. Formula corrections, where recorded, appear with their formulas above. Curation notes may also discuss corrections or unresolved interpretation. Consult the :doc:`review register ` for the checks and decisions.