Pressure broadening coefficients of H2O induced by CO2 for Venus atmosphere

Carbon dioxide (CO2) induced pressure broadening coefficients of water vapor (H2O) lines have been determined using a terahertz time-domain spectrometer (TDS). Thirty-two rotational transitions of H2O were observed in the spectral range of 18-102cm-1 (550-3050 GHz) for the first time. Using TDS allows one to measure absorption spectra with one order of magnitude better precision than Fourier transform spectrometer in this frequency region. The precision of our broadening coefficient measurements was 2.4% in average. The measured CO2 induced pressure broadening coefficients are compared to those calculated by the complex Robert-Bonamy formalism. The difference between the measurement and the theoretical estimation was in the range of -10.7% to +19.0% confirming the credibility of the theoretical approach. The impact on retrieval of water vapor abundance was examined by performing inversion analysis on H2O spectra of Venus atmosphere obtained with the Submillimeter Wave Astronomy Satellite. In this example case, the retrieved water vapor mixing ratio reduces by half at the altitude region of 70-85 km when applying the newly measured broadening coefficient compared to the air-broadening coefficient, and changes by 5% compared to that estimated by the complex Robert-Bonamy formalism.