ciddor_1996#

P. E. Ciddor, “Refractive index of air: new equations for the visible and near infrared”, Appl. Opt. 35, 1566 (1996)

Source record · Catalogue · Review register

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#

{
  "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 review register for the checks and decisions.