Johannes Lampel1,2
Comparison of different water vapour absorption line lists to measured atmospheric absorptions using ground-based MAX-DOAS , Aleksandra Kyuberis , Oleg Polyansky , Jonathan Tennyson , Denis Pöhler , Mingxi Yang , Martin Horbanski , Stefan Schmitt , Udo Frieß , Thomas Wagner , Ulrich Platt observations 4
4,5
5
1,2
6
1,2
1
1
3
1,2,3
(1) Heidelberg, Institute of Environmental Physics, Physics, Heidelberg, Germany (
[email protected]), (2) Airyx GmbH, Justus-von-Liebig-Str. 14, 69214 Eppelheim, Germany, (3) Max Planck Institute for Chemistry, 55128 Mainz, Germany, (4) Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia, (5) Department of Physics and Astronomy, University College London, Gower St, London WC1E 6BT, UK, (6) Plymouth Marine Laboratory,Prospect Place, Plymouth, PL1 3DH, UK Contact:
[email protected]
410 – 460nm: NO2, Glyoxal, Iodine monoxide
Line lists and Method
Type ai ai ai + exlbl
Citation Polyansky2018 Barber2006 Rothman2010
HITEMP rescaled Kyuberis HITRAN 2016
Rescaled based on MAX-DOAS obs. Work-in-Progress line list Most recent version of HITRAN H2O ll
ai + exlbl + exb ai ai + exlbl
Lampel2015 Not yet published Gordon2016
HONO
340 – 380nm: O4,HONO
Comment allowed first obs of UV abs. at 363nm Used in HITEMP and HITRAN 2012
Figure above: Between 410 and 458nm (for NO2) the rescaled HITRAN2012 line list, the Kyuberis line list and HITEMP are the best options judging from the obtained signal-to-noise ratios (S/N). Right figure: From 418 to 439nm the (ab-initio) Kyuberis line list predicts the absorption band shapes best. This range is used for the spectral retrieval of iodine monoxide (IO)
MAX-DOAS data was from two campaigns, based on the spectral coverage of the respective instrument and observed water vapour column densities. The spectral resolution of the data was around 0.5nm. Name
Location
Type
Instrument
Citation
M91 2012
Peruvian Upwelling (4 weeks)
Mostly clean MBL
430nm Airyx SkySpec
Lampel201 8
All spectral data was analysed in the same way, using different water vapour line lists. Literature cross-sections for other gases according to [Lampel2017].
Airyx SkySpec Instrument (previously: EnviMes)
Signal-to-noise ratios were determined from the fit results by dividing the H2O differential slant column density (dSCD) by ist fit error.
500 – 600nm: O3, OIO
Example fit from M91, 1°elevation, 4 min exp. Time. The thin lines are the respective fit residuals.
Conclusions The MAX-DOAS technique allows to compare quantitativly water vapour line lists in the UV/VIS range and Medium spectral resolution (0.5nm) is sufficient to ressolve different polyads up to 27800cm-1 (360nm) Recent advances on the field of ab-initio line lists for water vapour improved Prediction of absorption in the UV Prediction of relative band magnitudes in the blue wavelength range Signal-to-noise ratios from spectral data analysis: Allow to quantitatively compare agreement of line lists and observations Interferences with other absorbers cannot be excluded and require comparison of obtained column densities in different spectral intervals
O3 Δ dSCD [molec/cm2]
Comparison of signal-to-noise ratios (SN) using the different line lists reveals that the best fit is obtained using the POKAZATEL line list. Comparison of SN ratios provides first hints about the quality of the line list: 1. Absolute scaling of line intensities cancels out 2. Differences between modeled and observed absorptions result in reduction of SN ratio
Apparent glyoxal dSCDs are affected by the choice of the literature water vapour line list as shown on the right figure. While these differences of typically up to 3x1014 molec/cm2 are not crucial for urban observations of glyoxal [e.g. Volkamer et al 2007 Mexico City], it is known to be an issue for remote locations [Sinreich et al 2010, MBL]. However, for laboratory studies the influence was reported to be small [Thalman et al 2015].
Iodine dioxide (OIO) dSCDs as shown on the right retrieved at around 534565nm still show a linear behaviour in their water vapour interference. Therefore a strong influence of nonlinear behaviours due to saturation effects etc, can be exluded, despite large overlaying absorption structures.
40 ppb trop. ozone ~ 1018 molec cm-1
Ozone (NDACC reccomendation, 450-550nm): Even the broad absorption of ozone is sensitive to different water vapour line lists. From the signal-to-noise (S/N) comparison a clear selection of a ‚correct‘ data set is not possible, intercomparsions of inferred ozone concentrations from different wavelength ranges (e.g. UV) are needed.
As always, the correct dSCD is unknown. Surprisingly and contrary to the blue (around 440nm), the BT2 list shows here the highest S/N and also non-negative OIO dSCDs (shown below). Therefore, for the spectral range of OIO, everything but the POKAZATEL and Kyuberis line list could be an option.
Urban: >1ppb ~ 2.5 1016 molec/cm2 NO2 Pristine: 100ppt ~ 2.5 1015 molec/cm2 Glyoxal MBL:
