The effect of spectroscopic parameter inaccuracies on ground-based millimeter wave remote sensing of the atmosphere

- The sensitivity of retrievals to spectroscopic parameters is assessed.
- Air broadening parameters contribute the most to the error budget.
- O3 and N2O retrievals are sensitive to parameters of the target spectral lines.
- Many HNO3 lines in close proximity can cause large errors in HNO3 retrievals.
- ClO retrievals are sensitive to uncertainties in parameters of nearby O3 lines.

A sensitivity study was performed to assess the impact that uncertainties in the spectroscopic parameters of atmospheric species have on the retrieval of gas concentrations using the 265-280 GHz region of the electromagnetic spectrum. Errors in the retrieval of O3, N2O, HNO3, and ClO from spectra measured by ground-based radiometers were investigated. The goal of the study was to identify the spectroscopic parameters of these target species, and other interfering species, available in the JPL and HITRAN 2008 catalogues, which contribute the largest error to retrieved atmospheric concentration profiles in order to provide recommendations for new laboratory measurements. The parameters investigated were the line position, line strength, broadening coefficients and their temperature dependence, and pressure shift. Uncertainties in the air broadening coefficients of gases tend to contribute the largest error to retrieved atmospheric concentration profiles. For O3 and N2O, gases with relatively strong spectral signatures, the retrieval is sensitive to uncertainties in the parameters of the main spectral line that is observed. For HNO3, the uncertainties in many closely spaced HNO3 lines can cause large errors in the retrieved profile, and for ClO, the error in the profile is dominated by uncertainties in nearby, stronger O3 lines. Fourteen spectroscopic parameters are identified, for which updated measurements would have the most impact on the accuracy of ground-based remote sensing of the target species at 265-280 GHz.