Fig. 1. Fitting flow chart for harmonic signal based on WMS

Fig. 2. Variation of sensitivity δA of 2f/1f spectra to integrated absorbance A with A

Fig. 3. Variations of simulated normalized 2f/1f spectra with collisional width Δvc

Fig. 4. Variation of sensitivity δΔvc of 2f/1f spectrum to collisional width Δvc with Δvc

Fig. 5. Diagram of experimental setup

Fig. 6. Detected signal under the conditions of pressure of 101.325 kPa, temperature of 1000 K, and vapour mole fraction of 6.53%

Fig. 7. Updating processes of (a) A and (b) ΔvD or Δvc of two spectral lines

Fig. 8. Comparison of simulated and experimental 2f/1f signals of two spectral lines after fitting. (a) Spectral line 1; (b) spectral line 2

Fig. 9. (a) Measured temperature and vapour mole fraction at pressure of 101.325 kPa; (b) measured pressure and vapour mole fraction at temperature of 1000 K