NEW MEASUREMENTS OF THE WATER VAPOR ABSORPTION CROSS SECTION IN THE BLUE-VIOLET RANGE BY CAVITY-ENHANCED DIFFERENTIAL OPTICAL ABSORPTION SPECTROSCOPY

Abstract. The use of ro-vibronic spectra of I2 in the region of 543 nm to 578 nm as reference spectra for atmospheric Differential Optical Absorption Spectroscopy is studied. In this study it is shown that the retrieval of atmospheric column densities with Differential Optical Absorption Spectroscopy set-ups at FWHM at and above 1nm depends critically on the column density, under which the used reference spectrum was recorded. Systematic overestimation of the comparatively low atmospheric column density of I2 of the order of 13% is possible. Under low pressure conditions relevant in laboratory studies, the systematic deviations may grow up to 45%. To avoid such effects with respect to field measurements, new reference spectra of I2 were determined under column density of the order of 1016 molec/cm2 close to that expected for the atmospheric measurement. Thereby the described systematic deviations are avoided. Two typical configurations of Differential Optical Absorption Spectroscopy, which use grating spectrometers, were chosen for the spectroscopic set-up. One spectrum was recorded at similar resolution (0.25 nm FWHM) but finer binning (0.035 nm/pixel) than previously published data. For the other (0.59 nm FWHM, 0.154 nm/pixel) no previously published spectra exist. Wavelength calibration is accurate to ±0.04 nm and ±0.11 nm respectively. The absorption cross section for the recordings was determined under low column density with an accuracy of ±4% and ±3% respectively. The absolute absorption cross section of I2 at 500 nm (in standard air) in the continuum absorption region was determined using a method independent of iodine vapour pressure. Obtained was σI2(500 nm)=(2.186±0.021)·10−18 cm2·molec−1 in very good agreement with previously published results, but at 50% smaller uncertainty. From this and previously published results a weighted average of σI2(500 nm)=(2.191±0.02) ·10−18 cm2·molec−1 is determined.

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Effects of column density on I2 spectroscopy and a determination of I2 absorption cross section at 500 nm

Atmospheric Chemistry and Physics ◽

10.5194/acp-6-2177-2006 ◽

2006 ◽

Vol 6 (8) ◽

pp. 2177-2191 ◽

Cited By ~ 8

Author(s):

P. Spietz ◽

J. Gómez Martín ◽

J. P. Burrows

Keyword(s):

Optical Absorption ◽

Cross Section ◽

Absorption Spectroscopy ◽

Absorption Cross Section ◽

Column Density ◽

Differential Optical Absorption Spectroscopy ◽

Optical Absorption Spectroscopy ◽

Reference Spectrum ◽

Absorption Cross ◽

Atmospheric Column

Abstract. The use of ro-vibronic spectra of I2 in the region of 543 nm to 578 nm as reference spectra for atmospheric Differential Optical Absorption Spectroscopy is studied. It is shown that the retrieval of atmospheric column densities with Differential Optical Absorption Spectroscopy set-ups at FWHM at and above 1 nm depends critically on the column density, under which the used reference spectrum was recorded. Systematic overestimation of the comparatively low atmospheric column density of I2 of the order of 13% is possible. Under low pressure conditions relevant in laboratory studies, the systematic deviations may grow up to 45%. To avoid such effects with respect to field measurements, new reference spectra of I2 were determined under column density of the order of 1016 cm-2 close to that expected for an atmospheric measurement. Two typical configurations of Differential Optical Absorption Spectroscopy, which use grating spectrometers, were chosen for the spectroscopic set-up. One spectrum was recorded at similar resolution (0.25 nm FWHM) but finer binning (0.035 nm/pixel) than previously published data. For the other (0.59 nm FWHM, 0.154 nm/pixel) no previously published spectra exist. Wavelength calibration is accurate to ±0.04 nm and ±0.11 nm respectively. The absorption cross section for the recordings was determined under low column density with an accuracy of ±4% and ±3% respectively. The absolute absorption cross section of I2 at 500 nm (wavelength: in standard air) in the continuum absorption region was determined using a method independent of iodine vapour pressure. Obtained was σI2 (500 nm)=(2.186±0.021·10-18 cm2 in very good agreement with previously published results, but at 50% smaller uncertainty. From this and previously published results a weighted average of σI2(500 nm)=(2.191±0.02)·10-18 cm2 is determined.

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Measurement of atmospheric water vapor vertical column concentration and vertical distribution in Qingdao using multi-axis differential optical absorption spectroscopy

Acta Physica Sinica ◽

10.7498/aps.69.20200588 ◽

2020 ◽

Vol 69 (20) ◽

pp. 204204

Author(s):

Hong-Mei Ren ◽

Ang Li ◽

Zhao-Kun Hu ◽

Ye-Yuan Huang ◽

Jin Xu ◽

...

Keyword(s):

Water Vapor ◽

Optical Absorption ◽

Vertical Distribution ◽

Absorption Spectroscopy ◽

Differential Optical Absorption Spectroscopy ◽

Atmospheric Water Vapor ◽

Optical Absorption Spectroscopy ◽

Atmospheric Water ◽

Vertical Column

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Liquid water absorption and scattering effects in DOAS retrievals over oceans

Atmospheric Measurement Techniques ◽

10.5194/amt-7-4203-2014 ◽

2014 ◽

Vol 7 (12) ◽

pp. 4203-4221 ◽

Cited By ~ 19

Author(s):

E. Peters ◽

F. Wittrock ◽

A. Richter ◽

L. M. A. Alvarado ◽

V. V. Rozanov ◽

...

Keyword(s):

Optical Absorption ◽

Water Absorption ◽

Cross Section ◽

Absorption Spectroscopy ◽

Cross Sections ◽

Liquid Water ◽

Natural Waters ◽

Differential Optical Absorption Spectroscopy ◽

Optical Absorption Spectroscopy ◽

Offset Correction

Abstract. Spectral effects of liquid water are present in absorption (differential optical absorption spectroscopy – DOAS) measurements above the ocean and, if insufficiently removed, may interfere with trace gas absorptions, leading to wrong results. Currently available literature cross sections of liquid water absorption are provided in coarser resolution than DOAS applications require, and vibrational Raman scattering (VRS) is mostly not considered, or is compensated for using simulated pseudo cross sections from radiative transfer modeling. During the ship-based TransBrom campaign across the western Pacific in October 2009, MAX-DOAS (Multi-AXis differential optical absorption spectroscopy) measurements of light penetrating very clear natural waters were performed, achieving average underwater light paths of up to 50 m. From these measurements, the retrieval of a correction spectrum (H2Ocorr) is presented, compensating simultaneously for insufficiencies in the liquid water absorption cross section and broad-banded VRS structures. Small-banded structures caused by VRS were found to be very efficiently compensated for by the intensity offset correction included in the DOAS fit. No interference between the H2Ocorr spectrum and phytoplankton absorption was found. In the MAX-DOAS tropospheric NO2 retrieval, this method was able to compensate entirely for all liquid water effects that decrease the fit quality, and performed better than using a liquid water cross section in combination with a simulated VRS spectrum. The decrease in the residual root mean square (rms) of the DOAS fit depends on the measurement's contamination with liquid water structures, and ranges from ≈ 30% for measurements slightly towards the water surface to several percent in small angles above the horizon. Furthermore, the H2Ocorr spectrum was found to prevent misfits of NO2 slant columns, especially for very low NO2 scenarios, and thus increases the reliability of the fit. In test fits on OMI satellite data, the H2Ocorr spectrum was found selectively above ocean surfaces, where it decreases the rms by up to ≈ 11%.

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