Near-IR absorption of water vapor: Pressure dependence of line strengths and an upper limit for continuum absorption

Water vapor absorption cross-sections in the near-infrared region (10 500-10 800 cm−1) were measured using cavity ringdown spectroscopy. Linestrengths were measured for several absorption lines around 10 604 cm−1 (943 nm) between 500 and 850 Torr of N2 and found to be independent of pressure. Our measured linestrengths of these individual lines agree well with values from databases such as HITRAN and the ESA-WVR, which are currently used for atmospheric calculations, but the integrated strength over the entire measured spectral region is slightly larger than that contained in these databases. Water vapor pressure-broadening coefficients due to nitrogen were also estimated from these measurements. The absorption due to water vapor continuum was determined to be less than (9.2 ± 0.2) × 10−27 cm2 molecule−1 at 11 500 cm−1. This measured upper limit, though larger than the estimated values from continuum models, would not contribute significantly to the calculated radiation absorption in this wavelength region.