Measurement of H2O broadening of O2 A-band transitions and implications for atmospheric remote sensing.

We present laboratory measurements of H2O-broadened 16O2 A-band (b1Σg+ ← X3Σg–(0,0)) absorption spectra acquired with a laser-based photoacoustic spectroscopy method. This absorption band is widely used in a variety of high-precision atmospheric remote sensing applications. We report H2O broadening parameters for six of the strongest transitions in this band, and we show that these measured values are nominally 1.5–2 times greater than the corresponding air-broadening parameters. Simulations of atmospheric transmission spectra in the O2 A-band that incorporate our measured H2O broadening parameters indicate that H2O present at concentrations typically found in the Earth’s atmosphere can influence the column-integrated transmission relative to the dry air case. Further, because of spatial and seasonal variations in humidity, failure to account for the enhanced H2O pressure broadening effects can lead to concomitant biases in atmospheric O2 A-band retrievals of quantities such as surface pressure and path l...