Differential Optical Absorption Spectroscopy

Abstract

To cite this version:P. Spietz, J. Gómez Martín, J. P. Burrows. Effects of column density on I2 spectroscopy and a determination of I2 absorption cross section at 500 nm. Atmospheric Chemistry and Physics, European Geosciences Union, 2006, 6 (8), pp.2177-2191. <hal-00295944> Atmos. Chem. Phys., 6, 2177-2191, 2006 www.atmos-chem-phys.net/6/2177/2006 Abstract. The use of ro-vibronic spectra of I 2 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 I 2 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 I 2 were determined under column density of the order of 10 16 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 I 2 at 500 nm (wavelength: in standard air) in the continuum absorption region was determined using a method independent of iodine vapour pressure. Obtained was σ I 2 (500 nm)=(2.186±0.021)·10 −18 cm 2 in very good agreement with previously published results, but at 50% smaller uncertainty. From this and previously published results a weighted average of σ I 2 (500 nm)=(2.191±0.02)·10 −18 cm 2 is determined.

The version 3 OMI NO&lt;sub&gt;2&lt;/sub&gt; standard product

“…To calculate stratospheric and tropospheric AMFs, we use a pre-computed dimensionless scattering weight vector W (also known as the Box-AMF; Platt and Stutz, 2008). W describes the relationship between S for a column (stratospheric or tropospheric) and the local VCD, V i , in each atmospheric layer i within the column (Palmer et al, 2001;Martin et al, 2002):…”

“…Both products use the differential optical absorption spectroscopy (DOAS) spectral fitting approach (Platt and Stutz, 2008) to derive NO 2 slant column density (SCD), which represents the total NO 2 amount (molecules cm −2 ) along the average solar radiation path through the atmosphere as observed from OMI. After separation of tropospheric and stratospheric SCDs, these are converted to the respective NO 2 VCDs using model-derived air mass factors (AMFs): VCD = SCD/AMF.…”

High-resolution airborne imaging DOAS measurements of NO&lt;sub&gt;2&lt;/sub&gt; above Bucharest during AROMAT

“…Spectral calibration is performed using the emission lines of an HgCd spectrum and a high-resolution solar atlas (Kurucz et al, 1984). Subsequently, the DOAS method (Platt and Stutz, 2008) is applied to the calibrated spectra. Using an extraterrestrial solar spectrum as background spectrum in the DOAS analysis, as is done in some satellite retrievals, yields slant column densities (SCDs), which are the number densities of an absorber, integrated along the light path.…”

“…a large societal interest in knowing the amounts and spatial distributions, sources and sinks of NO x . NO 2 exhibits characteristic absorption structures in the UV-visible spectral range, enabling the application of the DOAS (Differential Optical Absorption Spectroscopy) method to measure column densities of this trace gas (Platt and Stutz, 2008).…”

Spatial distribution analysis of the OMI aerosol layer height: a pixel-by-pixel comparison to CALIOP observations

“…A spectral fit, prior to the OMI effective cloud retrieval algorithm, is performed over the 460-490 nm spectral range to derive the continuum reflectance R c (475 nm) and the O 2 −O 2 slant column density N s O2−O2 . This spectral fit relies on the differential optical spectroscopy (DOAS) approach (Platt and Stutz, 2008). N s O2−O2 represents the O 2 −O 2 absorption magnitude along the average light path through the atmosphere.…”