scholarly journals Measurement of atmospheric CO2 vertical column density using weighting function modified differential optical absorption spectroscopy

2013 ◽  
Vol 62 (13) ◽  
pp. 130703
Author(s):  
Sun You-Wen ◽  
Xie Pin-Hua ◽  
Xu Jin ◽  
Zhou Hai-Jin ◽  
Liu Cheng ◽  
...  
Keyword(s):  
Optical Absorption ◽  
Absorption Spectroscopy ◽  
Column Density ◽  
Weighting Function ◽  
Differential Optical Absorption Spectroscopy ◽  
Atmospheric Co2 ◽  
Optical Absorption Spectroscopy ◽  
Vertical Column ◽  
Vertical Column Density

scholarly journals Comparison of tropospheric NO<sub>2</sub> vertical columns in an urban environment using satellite, multi-axis differential optical absorption spectroscopy, and in situ measurements

2013 ◽  
Vol 6 (10) ◽  
pp. 2907-2924 ◽  
Author(s):  
D. Mendolia ◽  
R. J. C. D'Souza ◽  
G. J. Evans ◽  
J. Brook
Keyword(s):  
Optical Absorption ◽  
Urban Environment ◽  
Absorption Spectroscopy ◽  
Ground Level ◽  
Remotely Sensed ◽  
Differential Optical Absorption Spectroscopy ◽  
Optical Absorption Spectroscopy ◽  
Vertical Column ◽  
Above Ground Level

Abstract. Tropospheric NO2 vertical column densities have been retrieved and compared for the first time in Toronto, Canada, using three methods of differing spatial scales. Remotely sensed NO2 vertical column densities, retrieved from multi-axis differential optical absorption spectroscopy and satellite remote sensing, were evaluated by comparison with in situ vertical column densities estimated using a pair of chemiluminescence monitors situated 0.01 and 0.5 km a.g.l. (above ground level). The chemiluminescence measurements were corrected for the influence of NOz, which reduced the NO2 concentrations at 0.01 and 0.5 km by an average of 8 ± 1% and 12 ± 1%, respectively. The average absolute decrease in the chemiluminescence NO2 measurement as a result of this correction was less than 1 ppb. The monthly averaged ratio of the NO2 concentration at 0.5 to 0.01 km varied seasonally, and exhibited a negative linear dependence on the monthly average temperature, with Pearson's R = 0.83. During the coldest month, February, this ratio was 0.52 ± 0.04, while during the warmest month, July, this ratio was 0.34 ± 0.04, illustrating that NO2 is not well mixed within 0.5 km above ground level. Good correlation was observed between the remotely sensed and in situ NO2 vertical column densities (Pearson's R value ranging from 0.72 to 0.81), but the in situ vertical column densities were 52 to 58% greater than the remotely sensed columns. These results indicate that NO2 horizontal heterogeneity strongly impacted the magnitude of the remotely sensed columns. The in situ columns reflected an urban environment with major traffic sources, while the remotely sensed NO2 vertical column densities were representative of the region, which included spatial heterogeneity introduced by residential neighbourhoods and Lake Ontario. Despite the difference in absolute values, the reasonable correlation between the vertical column densities determined by three distinct methods increased confidence in the validity of the values provided by each measurement technique.

scholarly journals Extending differential optical absorption spectroscopy for limb measurements in the UV

2009 ◽  
Vol 2 (6) ◽  
pp. 2919-2982 ◽  
Author(s):  
J. Puķīte ◽  
S. Kühl ◽  
T. Deutschmann ◽  
U. Platt ◽  
T. Wagner
Keyword(s):  
Optical Absorption ◽  
Optical Depth ◽  
Absorption Spectroscopy ◽  
Weighting Function ◽  
A Priori ◽  
Differential Optical Absorption Spectroscopy ◽  
Optical Absorption Spectroscopy ◽  
A Priori Knowledge ◽  
Air Mass ◽  
Mass Factor

Abstract. Methods of UV/VIS absorption spectroscopy to determine the constituents in the Earth's atmosphere from measurements of scattered light are often based on the Beer-Lambert law, like e.g. Differential Optical Absorption Spectroscopy (DOAS). Therefore they are strictly valid for weak absorptions and narrow wavelength intervals (strictly only for monochromatic radiation). For medium and strong absorption (e.g. along very long light-paths like in limb geometry) the relation between the optical depth and the concentration of an absorber is not linear anymore. As well, for large wavelength intervals the wavelength dependent differences in the travelled light-paths become important, especially in the UV, where the probability for scattering increases strongly with decreasing wavelength. However, by taking into account these dependencies, the applicability of the DOAS method can be extended also to cases with medium to strong absorptions and for broader wavelength intervals. Common approaches for this correction are the so called air mass factor modified (or extended) DOAS and the weighting function modified DOAS. These approaches take into account the wavelength dependency of the slant column densities (SCDs), but also require a-priori knowledge for the air mass factor or the weighting function calculation by radiative transfer modelling. We describe an approach that considers the fitting results obtained from DOAS, the SCDs, as a function of wavelength and vertical optical depth and expands this function into a Taylor series of both quantities. The Taylor coefficients are then applied as additional fitting parameters in the DOAS analysis. Thus the variability of the SCD in the fit window is determined by the retrieval itself. This new approach gives a description of the SCD that is as close to reality as desired (depending on the order of the Taylor expansion), and is independent from any assumptions or a-priori knowledge of the considered absorbers. In case studies for simulated and measured spectra in the UV (332–357 nm), we demonstrate the improvement by this approach for the retrieval of vertical profiles of BrO from the SCIAMACHY limb observations. Compared to the standard DOAS approach, the results for BrO obtained from the simulated spectra are closer to the true profile, when applying the new method for the SCDs of ozone. Also for the measured spectra the agreement with validation measurements is improved significantly, especially for cases with strong ozone absorption. While the focus of this article is on the improvement of the BrO profile retrieval from the SCIAMACHY limb measurements, the novel approach may be applied for a wide range of DOAS retrievals.

scholarly journals Effects of column density on I<sub>2</sub> spectroscopy and a determination of I<sub>2</sub> absorption cross section at 500 nm

2005 ◽  
Vol 5 (4) ◽  
pp. 5183-5221 ◽  
Author(s):  
P. Spietz ◽  
J. C. 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. 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.

scholarly journals Validation of TROPOMI tropospheric NO<sub>2</sub> columns using dual-scan multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements in Uccle, Brussels

2020 ◽  
Vol 13 (10) ◽  
pp. 5165-5191 ◽  
Author(s):  
Ermioni Dimitropoulou ◽  
François Hendrick ◽  
Gaia Pinardi ◽  
Martina M. Friedrich ◽  
Alexis Merlaud ◽  
...  
Keyword(s):  
Optical Absorption ◽  
Absorption Spectroscopy ◽  
Vertical Profile ◽  
Elevation Angle ◽  
Differential Optical Absorption Spectroscopy ◽  
Optical Absorption Spectroscopy ◽  
Azimuthal Direction ◽  
Inversion Algorithm ◽  
Vertical Column ◽  
Near Surface

Abstract. Ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements of aerosols and tropospheric nitrogen dioxide (NO2) were carried out in Uccle (50.8∘ N, 4.35∘ E), Brussels, during 1 year from March 2018 until March 2019. The instrument was operated in both the UV and visible wavelength ranges in a dual-scan configuration consisting of two sub-modes: (1) an elevation scan in a fixed viewing azimuthal direction (the so-called main azimuthal direction) pointing to the northeast and (2) an azimuthal scan in a fixed low elevation angle (2∘). By applying a vertical profile inversion algorithm in the main azimuthal direction and a parameterization technique in the other azimuthal directions, near-surface NO2 volume mixing ratios (VMRs) and vertical column densities (VCDs) were retrieved in 10 different azimuthal directions. The dual-scan MAX-DOAS dataset allows for partly resolving the horizontal distribution of NO2 around the measurement site and studying its seasonal variations. Furthermore, we show that measuring the tropospheric NO2 VCDs in different azimuthal directions improves the spatial colocation with measurements from the Sentinel-5 Precursor (S5P), leading to a reduction of the spread in validation results. By using NO2 vertical profile information derived from the MAX-DOAS measurements, we also resolve a systematic underestimation in S5P NO2 data due to the use of inadequate a priori NO2 profile shape data in the satellite retrieval.

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