scholarly journals On the relative absorption strengths of water vapour in the blue wavelength range

2015 ◽  
Vol 8 (10) ◽  
pp. 4329-4346 ◽  
Author(s):  
J. Lampel ◽  
D. Pöhler ◽  
J. Tschritter ◽  
U. Frieß ◽  
U. Platt
Keyword(s):  
Water Vapour ◽  
Cross Sections ◽  
Spectral Region ◽  
Field Measurements ◽  
Optical Absorption Spectroscopy ◽  
Absorption Cross ◽  
Absorption Bands ◽  
Blue Wavelength ◽  
Water Vapour Absorption ◽  
Density Ratios

Abstract. In recent updates of the HITRAN water vapour H2O spectroscopic compilation covering the blue spectral region (here: 394–480 nm) significant changes for the absorption bands at 416 and 426 nm were reported. In order to investigate the consistency of the different cross-sections calculated from these compilations, H2O vapour column density ratios for different spectral intervals were retrieved from long-path and multi-axis differential optical absorption spectroscopy (DOAS) measurements. We observed a significant improvement of the DOAS evaluation when using the updated HITRAN water vapour absorption cross-sections for the calculation of the reference spectra. In particular the magnitudes of the residual spectra as well as the fit errors were reduced. However, we also found that the best match between measurement and model is reached when the absorption cross-section of groups of lines are scaled by factors ranging from 0.5 to 1.9, suggesting that the HITRAN water vapour absorption compilation still needs significant corrections. For this spectral region we present correction factors for HITRAN 2009, HITRAN 2012, HITEMP and BT2 derived from field measurements. Additionally, upper limits for water vapour absorption in the UV-A range from 330 to 390 nm are given.

scholarly journals On the relative absorption strengths of water vapour in the blue wavelength range

2015 ◽  
Vol 8 (6) ◽  
pp. 5895-5936 ◽  
Author(s):  
J. Lampel ◽  
D. Pöhler ◽  
J. Tschritter ◽  
U. Frieß ◽  
U. Platt
Keyword(s):  
Water Vapour ◽  
Cross Sections ◽  
Spectral Region ◽  
Field Measurements ◽  
Optical Absorption Spectroscopy ◽  
Absorption Cross ◽  
Absorption Bands ◽  
Blue Wavelength ◽  
Water Vapour Absorption ◽  
Density Ratios

Abstract. In recent updates of the HITRAN water vapour H2O spectroscopic compilation covering the blue spectral region (here: 394–480 nm) significant changes for the absorption bands at 416 and 426 nm were reported. In order to investigate the consistency of the different cross-sections calculated from these compilations, H2O vapour column density ratios for different spectral intervals were retrieved from Long-path and Multi-Axis – Differential Optical Absorption Spectroscopy (DOAS) measurements. We observed a significant improvement of the DOAS evaluation when using the updated HITRAN water vapour absorption cross-sections for the calculation of the reference spectra. In particular the magnitudes of the residual spectra as well as the fit errors were reduced. However we also found that the best match between measurement and model is reached when the absorption cross-section of groups of lines are scaled by factors ranging from 0.5 and 1.9, suggesting that the HITRAN water vapour absorption compilation still needs significant corrections. For this spectral region we present correction factors for HITRAN 2009, HITRAN 2012, HITEMP and BT2 derived from field measurements. Additionally, upper limits for water vapour absorption in the UV-A range from 330–390 nm are given.

scholarly journals Ground-based direct-sun DOAS and airborne MAX-DOAS measurements of the collision-induced oxygen complex, O<sub>2</sub>O<sub>2</sub>, absorption with significant pressure and temperature differences

2015 ◽  
Vol 8 (2) ◽  
pp. 793-809 ◽  
Author(s):  
E. Spinei ◽  
A. Cede ◽  
J. Herman ◽  
G. H. Mount ◽  
E. Eloranta ◽  
...  
Keyword(s):  
Cross Sections ◽  
Spectral Band ◽  
Specific Humidity ◽  
Optical Absorption Spectroscopy ◽  
Correction Factors ◽  
Absorption Cross ◽  
Atmospheric Conditions ◽  
Absorption Bands ◽  
Wide Range ◽  
Simultaneous Fitting

Abstract. The collision-induced O2 complex, O2O2, is a very important trace gas for understanding remote sensing measurements of aerosols, cloud properties and atmospheric trace gases. Many ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements of the O2O2 optical depth require correction factors of 0.75 ± 0.1 to reproduce radiative transfer modeling (RTM) results for a nearly pure Rayleigh atmosphere. One of the potential causes of this discrepancy is uncertainty in laboratory-measured O2O2 absorption cross section temperature and pressure dependencies due to difficulties in replicating atmospheric conditions in the laboratory environment. This paper presents ground-based direct-sun (DS) and airborne multi-axis (AMAX) DOAS measurements of O2O2 absorption optical depths under actual atmospheric conditions in two wavelength regions (335–390 and 435–490 nm). DS irradiance measurements were made by the Washington State University research-grade Multi-Function Differential Spectroscopy Instrument instrument from 2007 to 2014 at seven sites with significant pressure (778 to 1013 hPa) and O2O2 profile-weighted temperature (247 to 275 K) differences. Aircraft MAX-DOAS measurements were conducted by the University of Colorado (CU) AMAX-DOAS instrument on 29 January 2012 over the Southern Hemispheric subtropical Pacific Ocean. Scattered solar radiance spectra were collected at altitudes between 9 and 13.2 km, with O2O2 profile-weighted temperatures of 231 to 244 K and nearly pure Rayleigh scattering conditions. Due to the well-defined DS air-mass factors during ground-based measurements and extensively characterized atmospheric conditions during the aircraft AMAX-DOAS measurements, O2O2 "pseudo" absorption cross sections, σ, are derived from the observed optical depths and estimated O2O2 column densities. Vertical O2O2 columns are calculated from the atmospheric sounding temperature, pressure and specific humidity profiles. Based on the ground-based atmospheric DS observations, there is no pressure dependence of the O2O2 σ within the measurement errors (3%). Two data sets are combined to derive the peak σ temperature dependence of the 360 and 477 nm dimer absorption bands from 231 to 275 K. DS and AMAX-derived peak σ ( O2O2) as a function of T can be described by a quadratic function at 360 nm and linear function at 477 nm with about 9% ± 2.5% per 44 K rate. Recent laboratory-measured O2O2 cross sections by Thalman and Volkamer (2013) agree with these "DOAS apparent" peak σ( O2O2) at 233, 253 and 273 K within 3%. Changes in the O2O2 spectral band shape at colder temperatures are observed for the first time in field data. Temperature effects on spectral band shapes can introduce errors in the retrieved O2O2 column abundances if a single room temperature σ( O2O2) is used in the DOAS analysis. Simultaneous fitting of σ( O2O2) at temperatures that bracket the ambient temperature range can reduce such errors. Our results show that laboratory-measured σ( O2O2) (Hermans, 2011, at 296 K and Thalman and Volkamer, 2013) are applicable for observations over a wide range of atmospheric conditions. Column densities derived using Hermans (2011) σ at 296 K require very small correction factors (0.94 ± 0.02 at 231 K and 0.99 ± 0.02 at 275 K) to reproduce theoretically calculated slant column densities for DS and AMAX-DOAS measurements. Simultaneous fitting of σ( O2O2) at 203 and 293 K further improved the results at UV and visible wavelengths for AMAX-DOAS.

scholarly journals Detection of water vapour absorption around 363 nm in measured atmospheric absorption spectra and its effect on DOAS evaluations

2016 ◽  
Author(s):  
Johannes Lampel ◽  
Denis Pöhler ◽  
Oleg L. Polyansky ◽  
Aleksandra A. Kyuberis ◽  
Nikolai F. Zobov ◽  
...  
Keyword(s):  
Ab Initio ◽  
Water Vapour ◽  
Spectral Range ◽  
Visible Spectrum ◽  
Field Measurements ◽  
Absorption Lines ◽  
Optical Absorption Spectroscopy ◽  
Dissociation Limit ◽  
Water Vapour Absorption ◽  
Using Data

Abstract. Water vapour is known to absorb radiation from the microwave region to the blue part of the visible spectrum at a decreasing efficiency. Ab-initio approaches to model individual absorption lines of the gaseous water molecule predict absorption lines until its dissociation limit at 243 nm. We present first evidence of water vapour absorption near 363 nm from field measurements using data from Multi-Axis differential optical absorption spectroscopy (MAX-DOAS) and Longpath (LP)-DOAS measurements. The identification of the absorptions was based on the recent POKAZATEL line list by Polyansky et al. (2016). We observed absorption by water vapour at 363 nm with optical depths of up to 2 × 10−3. It correlates well with simultaneously measured well-established water vapour absorptions in the blue spectral range from 452–499 nm (R2 = 0.89), but the line intensities are underestimated by a factor of 2.6 &amp;pm; 0.5 by the ab-initio model. At a spectral resolution of 0.5 nm, we derive a maximum cross-section value of 2.7 × 10−27 cm2 molec−1 at 362.3 nm. The newly found absorption can have a significant impact on the spectral retrieval of absorbing trace-gas species in the spectral range around 363 nm. Its effect on the spectral analysis of O4, HONO and OClO is discussed.

scholarly journals Scattering and Absorption Cross-sections of Atmospheric Gases in the Ultraviolet-Visible Wavelength Range (307–725 nm)

2020 ◽  
Author(s):  
Quanfu He ◽  
Zheng Fang ◽  
Ofir Shoshamin ◽  
Steven S. Brown ◽  
Yinon Rudich
Keyword(s):  
Refractive Index ◽  
Wavelength Range ◽  
Cross Sections ◽  
Rayleigh Scattering ◽  
Dispersion Relations ◽  
Optical Absorption Spectroscopy ◽  
Absorption Cross ◽  
Atmospheric Gases ◽  
Scattering Cross ◽  
Scattering Cross Sections

Abstract. Accurate Rayleigh scattering and absorption cross-sections of atmospheric gases are essential for understanding the propagation of electromagnetic radiation in planetary atmospheres. Accurate extinction cross-sections are also essential for calibrating high finesse optical cavities and differential optical absorption spectroscopy and for accurate remote sensing. In this study, we measured the scattering and absorption cross-sections of carbon dioxide, nitrous oxide, sulfur hexafluoride, oxygen, and methane in the continuous wavelength range of 307–725 nm using Broadband Cavity Enhanced Spectroscopy (BBCES). The experimentally derived Rayleigh scattering cross-sections for CO2, N2O, SF6, O2, and CH4 agree with refractive index-based calculations, with a difference of 1.5 % and 1.1 %, 1.5 %, 2.9 %, and 1.4 % on average, respectively. The O2-O2 collision-induced absorption and absorption by methane are obtained with high precision at the 0.8 nm resolution of our BBCES instrument in the 307–725 nm wavelength range. New dispersion relations for N2O, SF6, and CH4 were derived using data in the UV-vis wavelength range. This study provides improved refractive index dispersion relations, n-based Rayleigh scattering cross-sections, and absorption cross-sections for these gases.

scholarly journals A broadband cavity ringdown spectrometer for in-situ measurements of atmospheric trace gases

2005 ◽  
Vol 5 (3) ◽  
pp. 3491-3532 ◽  
Author(s):  
M. Bitter ◽  
S. M. Ball ◽  
I. M. Povey ◽  
R. L. Jones
Keyword(s):  
Boundary Layer ◽  
Water Vapour ◽  
Marine Boundary Layer ◽  
Thermal Dissociation ◽  
Optical Absorption Spectroscopy ◽  
Integration Time ◽  
Research Station ◽  
Absorption Bands ◽  
Optical Extinction ◽  
Cavity Ringdown

Abstract. This paper describes a broadband cavity ringdown spectrometer and its deployment during the 2002 North Atlantic Marine Boundary Layer Experiment (NAMBLEX) to measure ambient concentrations of NO3, N2O5, I2 and OIO at the Mace Head Atmospheric Research Station, Co. Galway, Ireland. The effective absorption path lengths accessible with the spectrometer generally exceeded 10 km, enabling sensitive localised ''point'' measurements of atmospheric absorbers to be made adjacent to the other instruments monitoring chemically related species at the same site. For the majority of observations, the spectrometer was used in an open path configuration thereby avoiding surface losses of reactive species. A subset of observations targeted the N2O5 molecule by detecting the additional NO3 formed by the thermal dissociation of N2O5. In all cases the concentrations of the atmospheric absorbers were retrieved by fitting the differential structure in the broadband cavity ringdown spectra using a methodology adapted from long path differential optical absorption spectroscopy. The uncertainty of the retrieval depends crucially on the correct treatment and fitting of the absorption bands due to water vapour, a topic that is discussed in the context of analysing broadband cavity ringdown spectra. The quality of the measurements and the retrieval method are illustrated with representative spectra acquired during NAMBLEX in spectral regions around 660 nm (NO3 and N2O5) and 570 nm (I2 and OIO). Typical detection limits were 1 pptv for NO3 in an integration time of 100 s, 4 pptv for OIO and 20 pptv for I2 in an integration time of 10 min. Additionally, the concentrations of atmospheric water vapour and the aerosol optical extinction were retrieved in both spectral regions. A companion paper in this issue presents the time series of the measurements and discusses their significance for understanding the variability of short lived nitrogen and iodine compounds in the marine boundary layer.

scholarly journals MAX-DOAS formaldehyde slant column measurements during CINDI: intercomparison and analysis improvement

2013 ◽  
Vol 6 (1) ◽  
pp. 167-185 ◽  
Author(s):  
G. Pinardi ◽  
M. Van Roozendael ◽  
N. Abuhassan ◽  
C. Adams ◽  
A. Cede ◽  
...  
Keyword(s):  
Cross Sections ◽  
Cross Correlation ◽  
Optical Absorption Spectroscopy ◽  
Integration Time ◽  
Measuring Instruments ◽  
Absorption Cross ◽  
Correlation Effects ◽  
Data Set ◽  
Random Uncertainties ◽  
Ring Effect

Abstract. We present intercomparison results for formaldehyde (HCHO) slant column measurements performed during the Cabauw Intercomparison campaign of Nitrogen Dioxide measuring Instruments (CINDI) that took place in Cabauw, the Netherlands, in summer 2009. During two months, nine atmospheric research groups simultaneously operated MAX-DOAS (MultiAXis Differential Optical Absorption Spectroscopy) instruments of various designs to record UV-visible spectra of scattered sunlight at different elevation angles that were analysed using common retrieval settings. The resulting HCHO data set was found to be highly consistent, the mean difference between instruments generally not exceeding 15% or 7.5 × 1015 molec cm−2, for all viewing elevation angles. Furthermore, a sensitivity analysis was performed to investigate the uncertainties in the HCHO slant column retrieval when varying key input parameters such as the molecular absorption cross sections, correction terms for the Ring effect or the width and position of the fitting interval. This study led to the identification of potentially important sources of errors associated with cross-correlation effects involving the Ring effect, O4, HCHO and BrO cross sections and the DOAS closure polynomial. As a result, a set of updated recommendations was formulated for HCHO slant column retrieval in the 336.5–359 nm wavelength range. To conclude, an error budget is proposed which distinguishes between systematic and random uncertainties. The total systematic error is estimated to be of the order of 20% and is dominated by uncertainties in absorption cross sections and related spectral cross-correlation effects. For a typical integration time of one minute, random uncertainties range between 5 and 30%, depending on the noise level of individual instruments.

scholarly journals A miniDOAS instrument optimised for ammonia field-measurements

2016 ◽  
Author(s):  
J. Sintermann ◽  
K. Dietrich ◽  
C. Häni ◽  
M. Bell ◽  
M. Jocher ◽  
...  
Keyword(s):  
Cross Sections ◽  
Limit Of Detection ◽  
Moving Average ◽  
Field Measurements ◽  
Field Trials ◽  
Reference Spectrum ◽  
Absorption Cross ◽  
Local Regression ◽  
Pass Filter ◽  
Wide Range

Abstract. We present a DOAS instrument, called "miniDOAS", optimised for optical open-path field-measurements of ambient ammonia (NH3) alongside nitrogen oxide (NO) and sulphur dioxide (SO2). The instrument is a further development of the miniDOAS presented by Volten et al. (2012). Here, we use a temperature-controlled spectrometer, a deuterium light source and a modified optical arrangement. The system was set up in a robust, field-deployable, temperature-regulated housing. For the evaluation of light spectra we use a new high-pass filter routine based upon robust baseline extraction with local regression. In order to fit differential absorption cross-sections to the measurements, multiple linear regression is performed including terms of an autoregressive-moving-average model. For NH3 the instrument's precision is 0.8 to 1.4 %. Accuracy is larger than precision and derives from the precision, uncertainty in DOAS absorption cross-sections (± 3 %) and an uncertain estimation of concentration offsets (c0) present through the definition of reference spectrum I0. Accuracy will at minimum be approximately 0.3 μg m−3. The limit of detection against I0 is around 0.2 μg m−3. Comparisons of miniDOAS measurements to those by NH3 acid trap devices showed good agreement. The miniDOAS can be flexibly used for a wide range of field trials, such as micrometeorological NH3 flux measurements with approaches based upon horizontal or vertical concentration gradients. Results from such applications, covering concentration dynamics of sub-ppb to ppm mixing ratios, are presented.

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