Temperature and Pressure Dependence of High-Resolution Air-Broadened Absorption Cross Sections of NO_2(415−525 nm)

Abstract

Cross sections of air-broadened NO_2 in the 415−525 nm region are reported. These are retrieved from 21 absorption spectra recorded at 0.060 cm^(-1) resolution with the McMath−Pierce Fourier Transform Spectrometer located on Kitt Peak in Arizona. The measurements are obtained for pressures (1−760 Torr) and temperatures (220−298 K) that are representative of typical tropospheric and stratospheric conditions. Two sigma uncertainty (95% confidence interval ≈ 2σ_(mean)) for the absolute absorption cross sections is below ±7% over the reported wavelength range. The average integrated intensity of all our data is 〈σ〉_(400-500 nm) = 4.53 × 10^(-17) cm^2 nm, which is within 0.2% of the averaged value from the recent literature. The wavelength (referred to vacuum) accuracy is 0.011 cm^(-1) (2.8 × 10^(-4) nm at 500 nm) and precision is 0.0022 cm^(-1) throughout the investigated wavelength range. In agreement with previous observations, high-resolution features in the NO_2 absorption spectrum display a strong pressure dependence with an effective pressure broadening parameter of 0.116 ± 0.003 cm^(-1)/atm (the rate of increase of Lorentzian half width at half-maximum with pressure). Temperature has a relatively minor effect on the shapes of individual high-resolution features, but it exerts a complex dependence on the relative line intensities. Absorption cross sections reported here represent the highest resolution data available over a substantial (>100 nm) wavelength range for quantitative analysis of NO_2 atmospheric column absorption spectra.

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