Traceable total ozone column retrievals from direct solar spectral irradiance measurements in the ultraviolet

Total column ozone (TCO) is commonly measured by Brewer and Dobson spectroradiometers. Both types of instruments are using four wavelengths in the ultraviolet radiation range to derive TCO. For the calibration and quality assurance of the measured TCO both instrument types require periodic field comparisons with a reference instrument. This study presents traceable TCO retrievals from direct solar spectral irradiance measurements with the portable UV reference instrument QASUME. TCO is retrieved by a spectral fitting technique derived by a minimal least square fit algorithm using spectral measurements in the wavelength range between 305 nm and 345 nm. The retrieval is based on an atmospheric model accounting for different atmospheric parameters such as effective ozone temperature, aerosol optical depth, Rayleigh scattering, SO2, ground air pressure, ozone absorption cross sections and top-of-atmosphere solar spectrum. Traceability means, that the QASUME instrument is fully characterized and calibrated in the laboratory to SI standards (International System of Units). The TCO retrieval method from this instrument is independent from any reference instrument and does not require periodic in situ field calibration. The results show that TCO from QASUME can be retrieved with a relative standard uncertainty of less than 0.8 %, when accounting for all possible uncertainties from the measurements and the retrieval model, such as different cross sections, different reference solar spectra, uncertainties from effective ozone temperature or other atmospheric parameters. The long-term comparison of QASUME TCO with a Brewer and a Dobson in Davos, Switzerland, reveals, that all three instruments are consistent within 1 % when using the ozone absorption cross section from the University of Bremen. From the results and method presented here, other absolute SI calibrated cost effective solar spectroradiometers, such as array spectroradiometers, may be applied for traceable TCO monitoring.

The determination of the total ozone column using satellite measurements in the Chappuis ozone absorption bands over highly reflective underlying surfaces

<p>The total ozone column (TOC) is retrieved using multiple optical satellite instrumentation (including TOMS, OMI, TROPOMI, GOME, GOME-2, and SCIAMACHY, to name a few). The spatial resolution of total ozone satellite measurements is quite low (e.g., 7x3.5km for TROPOMI, 13x24km for OMI, and 30x60km for SCIAMACHY). In some cases (say, close to the ozone hole boundary) it is of importance to have information on the total ozone at a higher spatial resolution. In this work we propose the use of multiple optical instruments performing the measurements in the ozone Chappuis ozone bands (400-650nm) for the total ozone column determination. This makes it possible to extend the number of instruments, which can be used for the total ozone determination (say, also using current/historic measurements by MODIS/Aqua&Terra, S-GLI/SCOM-C, VIIRS/Suomi-NPP, MSI/S-2, OLCI/S-3, MERIS/ENVISAT). In particular, MERIS and SCIAMACHY have been operated from the same satellite platform and had similar swaths (960km for SCIAMACHY and 1150km for MERIS). This means the method of total ozone retrieval based on combination of SCIAMACHY (30x60km) and MERIS (0.3x0.3km) observations over highly reflective ground (say, in Antarctica, where the ozone hole is located) is of value. The total ozone retrievals using Chappuis ozone bands is based on the fact that the top-of-atmosphere reflectance observed over a highly reflective ground (say, snow) has a minimum in the visible located around 600nm. This feature is due to due to the absorption of light by the atmospheric ozone (Gorshelev et al., 2014). The contribution of both ground and atmospheric light scattering to the top-of-atmosphere (TOA) does not have extrema in the vicinity of 600nm. Therefore, there is a possibility to remove both atmospheric and ground light scattering effects to the TOA reflectance over highly reflective underlying surface and derive the atmospheric transmittance due to the ozone absorption effects, which can be used for the TOC determination. Such a method has been explored using MERIS/ENVISAT (Jolivet et al., 2016) and OLCI/S-3 (Kokhanovsky et al., 2020) in the past. This paper is aimed at further improvement of the technique as applied to OLCI/S-3A,B. We have performed intercomparisons of OLCI TOC retrievals with TOC derived from ground and other satellite (e.g., OMI, TROPOMI, GOME-2) measurements. The TOC retrievals using OLCI have been performed over entire Antarctica allowing the generation of TOC at various spatial resolutions including standard 1x1 degree resolution.</p><p>Gorshelev, V., et al., 2014: High spectral resolution ozone absorption cross-sections – Part 1: Measurements, data analysis and comparison with previous measurements around 293 K, Atmos. Meas. Tech., 7, 609–624, https://doi.org/10.5194/amt-7-609-2014.</p><p>Jolivet D., et al., 2016: TORMS : total ozone retrieval from MERIS in view of application to Sentinel-3,  Living Planet Symposium, Proceedings of the conference held 9-13 May 2016 in Prague, Czech Republic. Edited by L. Ouwehand. ESA-SP Volume 740, ISBN: 978-92-9221-305-3, p.358</p><p>Kokhanovsky, A. A., et al., 2020: Retrieval of total ozone over Antarctica using Sentinel -3 Ocean and Land Colour Instrument, JQSRT, 2020, 251, https://doi.org/10.1016/j.jqsrt.2020.107045.</p><p> </p>

Consistency of total column ozone measurements between the Brewer and Dobson spectroradiometers of the LKO Arosa and PMOD/WRC Davos

Total column ozone measured by Brewer and Dobson spectroradiometers at Arosa and Davos, Switzerland, have systematic seasonal variations of around 1.5 % using the standard operational data processing. Most of this variability can be attributed to the temperature sensitivity of approx. +0.1 %/K of the ozone absorption coefficient of the Dobson spectroradiometer (in this study D101). While the currently used Bass&Paur ozone absorption cross-sections produce inconsistent results for Dobson and Brewer, the use of the ozone absorption cross-sections from Serdyuchenko et al. (2013) in conjunction with an effective ozone temperature dataset produces excellent agreement between the investigated four Brewers (of which two double Brewers), and Dobson D101. Even though other ozone absorption cross-sections available in the literature are able to reduce the seasonal variability, all of those investigated produce systematic biases in total column ozone between Brewer and Dobson of 1.1 % to 3.1 %. The highest consistency of total column ozone from Brewers and Dobson D101 at Arosa/Davos of 0.1 % is obtained by applying the Rayleigh scattering cross-sections from Bodhaine et al. (1999), the ozone absorption cross-sections from Serdyuchenko et al. (2013), the effective ozone temperature from either ozonesondes or ECMWF, and the measured line-spread functions of Brewer and Dobson. The variability between Brewer and Dobson for single measurements of 0.9 % can be reduced to less than 0.5 % for monthly means and 0.3 % on yearly means. As show here, the proposed methodology produces consistent total column ozone datasets between Brewer and Dobson spectroradiometers of better than 1 %. For colocated Brewer and Dobson spectroradiometers, as is the case for the Arosa/Davos total column ozone times series, this allows the merging of these two distinct datasets to produce a homogeneous time series of total column ozone measurements. Furthermore, it guarantees the long-term future of this longest total column ozone time-series, by proposing a methodology how to eventually replace the ageing Dobson spectroradiometer with the state-of-the art Brewer spectroradiometer.

Impact of using a new ultraviolet ozone absorption cross-section dataset on OMI ozone profile retrievals

We evaluate different sets of high-resolution ozone absorption cross-section data for use in atmospheric ozone profile measurements in the Hartley and Huggins bands with a particular focus on BDM 1995 (Daumont et al. 1992; Brion et al., 1993; Malicet et al., 1995), currently used in our retrievals, and a new laboratory dataset by Birk and Wagner (2018) (BW). The BDM cross-section data have been recommended to use for retrieval of ozone profiles using spaceborne nadir-viewing backscattered ultraviolet (BUV) measurements since its improved performance was demonstrated against other cross-sections including Bass and Paur (1985) (BP) and those of Serdyuchenko et al. (2014) and Gorshelev et al. (2014) (SER) by the “Absorption Cross-Sections of Ozone” (ACSO) activity. The BW laboratory data were recently measured within the framework of the European Space Agency (ESA) project SEOM-IAS (Scientific Exploitation of Operational Missions – Improved Atmospheric Spectroscopy Databases) to provide an advanced absorption cross-section database. The BW cross-sections are made from measurements at more temperatures and in a wider temperature range than BDM, especially for low temperatures. Relative differences of cross-sections between BW and BDM range from ∼2 % at shorter UV wavelengths to ∼5 % at longer UV wavelengths at warm temperatures. Furthermore, these differences dynamically increase by up to ±40 % at cold temperatures due to no BDM measurements having been made below 218 K. We evaluate the impact of using different cross-sections on ozone profile retrievals from Ozone Monitoring Instrument (OMI) measurements. Correspondingly, this impact leads to significant differences in individual ozone retrievals by up to 50 % in the tropopause where the coldest atmospheric temperatures are observed. Bottom atmospheric layers illustrate the significant change of the retrieved ozone values, with differences of 20 % in low latitudes, which is not the case in high latitudes because the ozone retrievals are mainly controlled by a priori ozone information in high latitudes due to less photon penetration down to the lower troposphere. Validation with ozonesonde observations demonstrates that BW and BDM retrievals show altitude-dependent bias oscillations of similar magnitude relative to ozonesonde measurements, much smaller than those of both BP and SER retrievals. However, compared to BDM, BW retrievals show significant reduction in standard deviation, by up to 15 %, especially at the coldest atmospheric temperatures. Such improvement is achieved mainly by the better characterization of the temperature dependence of ozone absorption.

Treatment of Bio-Treated Coking Wastewater by Catalytic Ozonation with Semi-Batch and Continuous Flow Reactors

In this work, the treatment of bio-treated coking wastewater (BCW) by catalytic ozonation was conducted in semi-batch and continuous flow reactors. The kinetics of chemical oxygen demand (COD) removal were analyzed using BCWs from five coking plants. An integral reactor with catalytic ozonation stacked by ozone absorption (IR) was developed, and its efficiency was studied. The catalyst of MnxCe1-xO2/γ-Al2O3 was efficient in the catalytic ozonation process for the treatment of various BCWs. The chemical oxygen demand (COD) removal efficiencies after 120 min reaction were 64–74%. The overall apparent reaction rate constants were 0.0101–0.0117 min−1, which has no obvious relationship with the initial COD of BCW and pre-treatment biological process. The IR demonstrated the highest efficiency due to the enhancement of mass transfer and the utilization efficiency of ozone. Bypass internal circulation can further improve the reactor efficiency. The optimal results were obtained with the ozone absorption section accounting for 19% of the valid water depth in the reactor and 250% of circulation flow ratio. The long-term and full-scale application of the novel reactor in a continuous mode indicated stable removal of COD and polycyclic aromatic hydrocarbons (PAHs). The results showed that the system of IR is a promising reactor type for tertiary treatment of coking wastewater by catalytic ozonation.

Impact of using a new ultraviolet ozone absorption cross-section dataset on OMI ozone profile retrievals

We evaluate different sets of high-resolution ozone absorption cross-section data for use in atmospheric ozone profile measurements in the Hartley and Huggins bands with a particular focus on Brion-Daumont-Malicet et al. (1995) (BDM) currently used in our retrievals, and a new laboratory dataset by Birk and Wagner (BW) (2018). The BDM cross-section data have been recommended to use for retrieval of ozone profiles using spaceborne nadir viewing Backscattered UltraViolet (BUV) measurements since its improved performance was demonstrated against other cross-sections including Bass and Paur (1985) (BP) and those of Serdyuchenko et al (2014) and Gorshelev et al. (2014) (SER) by the Absorption Cross-Sections of Ozone (ACSO) activity. The BW laboratory data were recently measured within the framework of the ESA project SEOM-IAS (Scientific Exploitation of Operational Missions – Improved Atmospheric Spectroscopy Databases) to provide an advanced absorption cross-section database. The BW cross-sections are made from measurements at more temperatures and in a wider temperature range than BDM, especially for low temperatures. Compared to BW, BDM cross-sections are positively biased from ~2 % at shorter UV to ~5 % at longer UV at warm temperatures. Furthermore, these biases dynamically increase by up to ± 40 % at cold temperatures due to no BDM measurements below 218 K. We evaluate the impact of using different cross-sections on ozone profile retrievals from Ozone Monitoring Instrument (OMI) measurements. Correspondingly, this impact leads to significant differences in individual ozone retrievals by up to 50 % in the tropopause where the coldest atmospheric temperature is observed. Bottom atmospheric layers illustrate the significant change of the retrieved ozone values with biases of 20 % in low latitudes, which is not the case in high latitudes because the ozone retrievals are mainly controlled by a priori ozone information in high latitudes due to less photon penetration down to the lower troposphere. Validation with ozonesonde observations demonstrates that BW and BDM retrievals show altitude-dependent bias oscillations of similar magnitude relative to ozonesonde measurements, much smaller than those of both BP and SER retrievals. However, compared to BDM, BW retrievals show significant reduction in standard deviation by up to 15 %, especially at the coldest atmospheric temperature. Such improvement is achieved mainly by th better characterization of the temperature dependence of ozone absorption.