Ozone Absorption Cross Section Research Articles

A brief introduction and some background to the article JQSRT 1998;60:1025–31 and its companion

This note provides a short introduction, some background information and relevant history related to reprint of the article “Atmospheric remote-sensing reference data from GOME: Part 1. Temperature-dependent absorption cross-sections of NO 2 in the 231–794 nm range” (JQSRT 1998;60:1025–31). The article and its companion “Atmospheric remote-sensing reference data from GOME: 2. Temperature-dependent absorption cross sections of O 3 in the 231–794 nm range” (JQSRT 1999;61:509–17) provided timely and unique data sets of the absorption cross sections of Nitrogen dioxide, NO 2, and ozone, O 3. The reported absorption cross sections have a spectral resolution sufficient to distinguish the electronic vibrational and rotational features of NO 2 and O 3 and were made in the temperature range of relevance to the earth's atmosphere, viz. 200–300 K, over a wide spectral range. These species are two of the most important trace gases in earth's atmosphere, and play key roles in determining the chemistry and dynamics of the earth's atmosphere and the conditions at the earth's surface experienced by the biosphere. Whilst providing valuable information about the electronic states of NO 2 and O 3, these spectra were determined primarily for their exploitation in the retrieval of trace gases from measurements of solar back scattered radiation by ground based and space borne instrumentation. These yield the local and global amounts and distributions of NO 2 and O 3, thereby constraining our knowledge about atmospheric chemistry and dynamics and the impact of pollution from the local to the global scale. The measurement, publication and use of these spectral sets are among many important milestones in the development of atmospheric remote sensing.

Temperature and slant path effects in Dobson and Brewer total ozone measurements

There is a worldwide tendency to replace Dobson spectrophotometers in ground‐based total ozone (TOZ) measurements by more advanced Brewer spectrophotometers. Ensuring the homogeneity of these data sets is of utmost importance if changes in TOZ of a few percent over long time periods are to be diagnosed accurately. Previous studies have identified a seasonal bias of a few percent between midlatitude Brewer and Dobson measurements. At Arosa (Switzerland), two Dobson and three Brewer instruments have been colocated since 1998, providing a unique data set of quasi‐simultaneous observations, invaluable to study systematic differences between these measurements. The differences are partially attributed to the seasonal variability in atmospheric temperatures and ozone slant paths (OSP). The sensitivity to the temperature dependence of the ozone absorption cross section is calculated for each operational Brewer spectrophotometers at Arosa by using different high‐ and low‐resolution reference spectra appropriately weighted with the instruments' slit functions, whereas the information on the primary standard instruments is used for all the Dobson instruments. The Brewer retrieval algorithm reveals a higher sensitivity to the reference spectra applied than the Dobson. When adopting the Bass and Paur (1985) or Malicet et al. (1995) ozone absorption spectra with their specific temperature dependence, and correcting for the OSP effect, the seasonal bias between Dobson and Brewer TOZ measurements is reduced to 0.6%. Conversely, these differences increase when using the spectral data of Burrows et al. (1999). This finding illustrates that the accuracy of ground‐based spectrophotometric TOZ measurements is limited by the uncertainty in the ozone cross sections measured by different internationally leading laboratories.

Towards a better representation of the solar cycle in general circulation models

Abstract. We introduce the improved Freie Universität Berlin (FUB) high-resolution radiation scheme FUBRad and compare it to the 4-band standard ECHAM5 SW radiation scheme of Fouquart and Bonnel (FB). Both schemes are validated against the detailed radiative transfer model libRadtran. FUBRad produces realistic heating rate variations during the solar cycle. The SW heating rate response with the FB scheme is about 20 times smaller than with FUBRad and cannot produce the observed temperature signal. A reduction of the spectral resolution to 6 bands for solar irradiance and ozone absorption cross sections leads to a degradation (reduction) of the solar SW heating rate signal by about 20%. The simulated temperature response agrees qualitatively well with observations in the summer upper stratosphere and mesosphere where irradiance variations dominate the signal. Comparison of the total short-wave heating rates under solar minimum conditions shows good agreement between FUBRad, FB and libRadtran up to the middle mesosphere (60–70 km) indicating that both parameterizations are well suited for climate integrations that do not take solar variability into account. The FUBRad scheme has been implemented as a sub-submodel of the Modular Earth Submodel System (MESSy).

A study of systematic biases and measurement uncertainties in ozone mole fraction measurements with the NIST Standard Reference Photometer

Sources of bias in the National Institute of Standards and Technology ozone Standard Reference Photometer (SRP) maintained by the Bureau International des Poids et Mesures have been investigated. A relative bias of −0.4% in the ozone mole fraction measurement caused by a temperature gradient in the gas cells of the instrument was characterized and corrected for in a modified version of the instrument. A second relative bias of +0.5% due to the multiple reflections of light within the gas cells was also corrected. The Guide to the Expression of Uncertainty in Measurement approach was used to develop an uncertainty budget for the modified SRP, including a relative value for the ozone absorption cross-section uncertainty of 2.1% (k = 2). The measurement uncertainty for the bias-corrected SRPs is enlarged compared with earlier studies, but their comparability improved.

Absolute cross sections of ozone at atmospheric temperatures for the Wulf and the Chappuis bands

Ozone absorption constitutes a variable background against which measurement of pollution is observed from satellites by the solar occultation technique. The temperature-altitude gradient of ozone spans the range 180-340 K. Laboratory measurements of ozone absorption at temperatures across this range are needed to calibrate spectroscopic remote sensing, but have yielded results in substantial disagreement with each other. This paper presents the first measurements of the variation of absorption cross-sections of ozone at temperatures from 144 to 300 K over the 9250-18 500 cm(-1) spectral region.

Bias in Dobson total ozone measurements at high latitudes due to approximations in calculations of ozone absorption coefficients and air mass

The Dobson spectrophotometer is the primary standard instrument for ground‐based measurements of total column ozone. The accuracy of its data depends on the knowledge of ozone absorption coefficients used for data reduction. We document an error in the calculations that led to the set of absorption coefficients currently recommended by the World Meteorological Organisation (WMO). This error has little effect because an empirical adjustment was applied to the original calculations before the coefficients were adopted by WMO. We provide evidence that this adjustment was physically sound. The coefficients recommended by WMO are applied in the Dobson network without correction for the temperature dependence of the ozone absorption cross sections. On the basis of data measured by Dobson numbers 80 and 82, which were operated by the National Oceanic and Atmospheric Administration (NOAA) Climate Monitoring and Diagnostics Laboratory at the South Pole, we find that omission of temperature corrections may lead to systematic errors in Dobson ozone data of up to 4%. The standard Dobson ozone retrieval method further assumes that the ozone layer is located at a fixed height. This approximation leads to errors in air mass calculations, which are particularly relevant at high latitudes where ozone measurements are performed at large solar zenith angles (SZA). At the South Pole, systematic errors caused by this approximation may exceed 2% for SZAs larger than 80°. The bias is largest when the vertical ozone distribution is distorted by the “ozone hole” and may lead to underestimation of total ozone by 4% at SZA = 85° (air mass 9). Dobson measurements at the South Pole were compared with ozone data from a collocated SUV‐100 UV spectroradiometer and Version 8 overpass data from NASA's Total Ozone Mapping Spectrometer (TOMS). Uncorrected Dobson ozone values tend to be lower than data from the two other instruments when total ozone is below 170 Dobson units or SZAs are larger than 80°. When Dobson measurements are corrected for the temperature dependence of the ozone absorption cross section and accurate air mass calculations are implemented, data from the three instruments agree with each other to within ±2% on average and show no significant dependence on SZA or total ozone.

Ozone column classified climatology of ozone and temperature profiles based on ozonesonde and satellite data

An updated and atmospheric dynamics oriented global climatology of ozone profiles has been derived from ozonesonde and satellite observations. The climatology, which uses total ozone to parameterize the profile shape, provides improved a priori information for ozone profile retrieval from satellite measurements using optimal estimation. It can be also used to correct the profile shape error in total ozone retrieval. Sonde data were selected from the 1990–2000 and 1988–1999 period for SAGE II excluding two years of SAGE II V6.1 data influenced by the Mount Pinatubo eruption in 1991. In addition, POAM III V3 data covering the polar region and SHADOZ ozonesonde data in the tropics were included. The ozone profile data were binned in steps of 30 DU of total ozone, 30° wide zonal bands, and into a six‐month season (winter/spring and summer/fall) in middle and high latitudes. No seasonal distinction is needed in the low‐latitude region (30°S to 30°N). Mean and standard deviation profiles for each ozone class were combined from satellites and sondes with a transition region in the range 20–26 km to merge both data sets. Temperature data from sonde, SAGE II collocated NMC, and POAM III collocated UKMO, where NMC and UKMO data are used in respective ozone retrieval, have been binned and averaged in the same manner as the ozone profiles so that for each mean ozone profile a matching temperature profile was derived. Corresponding ozone and temperature profiles help in accounting for the temperature dependence of the ozone absorption cross sections in the retrieval process. Key features of both ozone and temperature climatologies are discussed. As examples, ozone‐temperature correlation and the climatology of tropopause heights as derived from this climatology are presented, and they serve as diagnostic tools to show that the new climatology is a representative data set for global applications. Good agreement between collocated sonde profiles from Hohenpeissenberg (47.8°, 11.0°) and GOME ozone profiles, retrieved using optimal estimation method and using this climatology as constraints, was found. Also, comparison with GOME results, which were retrieved using a zonal monthly mean climatology, demonstrates the large improvements achieved by using this new climatology, particularly in the lowermost stratosphere and tropopause region.

Temperature‐dependent absorption cross sections of ozone in the Wulf‐Chappuis band at 759–768 nm

Absorption cross sections of ozone in the Wulf‐Chappuis band at 759–768 nm have been determined using cavity ring‐down spectroscopy at 215–298 K. Precise measurements at 762.07 and 764.47 nm revealed a slight temperature dependence of the absorption cross sections: (762.07 nm, 298 K) = (2.86 ± 0.04) × 10−22 cm2 molecule−1; (762.07 nm, 215 K) = (2.62 ± 0.04) × 10−22; (764.47 nm, 296 K) = (2.70 ± 0.03) × 10−22; and (764.47 nm, 214 K) = (2.44 ± 0.03) × 10−22. Results at 762.07 nm are indistinguishable within the experimental uncertainties from those reported by Burkholder and Talukdar [1994]. Results from the present work facilitate a more accurate retrieval of atmospheric temperature, cloud height, and cloud coverage data from satellite measurements of absorption by O2 in the A band around 761 nm.

A Fast Delivery system for the retrieval of near real-time ozone columns from GOME data

A Fast Delivery (FD) system has been developed to provide GOME (Global Ozone Monitoring Experiment) total ozone columns within 3 h after observation. This meets the growing demand for near real-time ozone products for applications such as the assimilation of ozone in Numerical Weather Prediction (NWP) models, monitoring the status of the ozone layer and improving surface UV radiation forecasts. The FD system uses only a small part of the raw GOME data that are available in near real-time. The FD level 0 to 1 and level 1 to 2 processors are based on algorithms as used within the off-line ESA/DLR GOME Data Processor (GDP). However, several changes in the algorithms have been made to improve the retrieval of the ozone columns: (1) the use of effective ozone absorption cross-sections based on ECMWF (the European Centre for Medium-Range Weather Forecasts) temperature forecast in the ozone slant column fit, (2) the use of the DAK radiative transfer model and the Fortuin and Kelder ozone climatology for the air mass factor calculations and (3) the use of the FRESCO (Fast Retrieval Scheme for Cloud Observables) cloud algorithm. The accuracy of the FD ozone columns has been determined by a pseudo-global validation study involving ground-based total ozone observations from about 15 NDSC (Network for the Detection of Stratospheric Change) sites. There is a reasonable general agreement with the ground-based measurements (within 5% for low and mid latitudes, within m 10 to +5% for high latitudes) and the level of quality meets the requirements for near real-time applications.

A new accurate wavelength calibration for the ozone absorption cross section in the near‐UV spectral region, and its effect on the retrieval of BrO from measurements of zenith‐scattered sunlight

Measurements of BrO in the atmosphere are now routinely made using UV absorption spectroscopy, but it has recently been noted that the retrieved BrO amounts are critically dependent on the wavelength dependence of the ozone absorption cross sections used in the retrieval procedure (ozone absorbs in the same wavelength region and must therefore be accounted for in the analysis). Although atmospheric BrO measurements are typically made at a spectral resolution of ∼1 nm, it has been shown that an inaccuracy of just 0.02 nm in the wavelength calibration of the ozone cross section can result in large errors in the retrieved BrO amount. Ozone absorption cross sections calibrated to <10−3 nm are presented here in the wavelength region generally used for the retrieval of BrO from observations of scattered solar radiation (345–360 nm), and for a wide range of temperatures (223–292 K). This level of accuracy in the wavelength calibration was achieved using Fourier transform spectroscopy, to record ozone absorption spectra at a maximum instrument resolution of 1.0 cm−1. Comparisons of these well‐calibrated cross sections with those currently in general use for measurements of BrO, that is, those measured for the Global Ozone Monitoring Experiment (GOME) satellite instrument, reveal that the GOME cross sections must be shifted by an amount in the range +0.02 to +0.03 nm in order to correct their wavelength calibration. This correction to the wavelength calibration is shown to result in a significant reduction (10–20%) in the column amounts of BrO retrieved from ground‐based measurements of zenith‐scattered sunlight. An additional decrease of 5–10% is seen when the high‐resolution cross sections reported here replace the GOME wavelength‐corrected cross sections in the analysis procedure, reducing estimates of total atmospheric BrO correspondingly.

Monitoring O_3 with solar-blind Raman lidars

The benefits of retrieving ozone concentration profiles by a use of a single Raman signal rather than the Raman differential absorption lidar (DIAL) technique are investigated by numerical simulations applied either to KrF- (248 nm) or to quadrupled Nd:YAG- (266 nm) based Raman lidars, which are used for both daytime and nighttime monitoring of the tropospheric water-vapor mixing ratio. It is demonstrated that ozone concentration profiles of adequate accuracy and spatial and temporal resolution can be retrieved under low aerosol loading by a single Raman lidar because of the large value of the ozone absorption cross section both at 248 nm and at 266 nm. Then experimental measurements of Raman signals provided by the KrF-based lidar operating at the University of Lecce (40 degrees 20'N, 18 degrees 6'E) are used to retrieve ozone concentration profiles by use of the Raman DIAL technique and the nitrogen Raman signal.

Validation of 3 years of ozone measurements over Network for the Detection of Stratospheric Change station Lauder, New Zealand

A large number of ozone profiles measured by using various methods (lidar, ozonesondes, microwave radiometer, and Stratospheric Aerosol and Gas Experiment II) over Lauder, New Zealand, between late 1994 and early 1998 are intercompared. These profiles are also used to validate a collocated Dobson spectrophotometer. Between March 1996 (August 1996 for sonde measurements) and January 1998, all instruments were operational and no instrument changes took place. The ozone number densities averaged over this period agreed within 5% in the 20‐ to 35‐km range. Between 12 and 20 km, lidar and sonde results deviated by less than 8%, and lidar and SAGE II results deviated by less than 15%. The ozone column densities measured by the Dobson spectrophotometer agreed within 3% with the integrated ozone profiles. The various methods are discussed, and modifications are proposed. They comprise a decrease of the reported sonde altitudes of about 125 m (±50 m) to correct for the response time of the sonde's chemical solution, the use of more accurate molecular parameter values in the lidar algorithm, and a 2.5% decrease in SAGE II ozone densities. Improved agreement between the average ozone profiles to within 1.5% for lidar and sondes (20–35 km) and within 2.5% for lidar and SAGE II (20–35 km) is achieved. The Dobson results are found to be influenced by the annual cycle of the temperature profile through the altitude‐averaged ozone absorption cross section, which has been assumed to be constant in the presented data but actually varies with an amplitude of 2% over Lauder.

Solar energy deposition rates in the mesosphere derived from airglow measurements: Implications for the ozone model deficit problem

We derive rates of energy deposition in the mesosphere due to the absorption of solar ultraviolet radiation by ozone. The rates are derived directly from measurements of the 1.27‐μm oxygen dayglow emission, independent of knowledge of the ozone abundance, the ozone absorption cross sections, and the ultraviolet solar irradiance in the ozone Hartley band. Fifty‐six months of airglow data taken between 1982 and 1986 by the near‐infrared spectrometer on the Solar‐Mesosphere Explorer satellite are analyzed. The energy deposition rates exhibit altitude‐dependent annual and semi‐annual variations. We also find a positive correlation between temperatures and energy deposition rates near 90 km at low latitudes. This correlation is largely due to the semiannual oscillation in temperature and ozone and is consistent with model calculations. There is also a suggestion of possible tidal enhancement of this correlation based on recent theoretical and observational analyses. The airglow‐derived rates of energy deposition are then compared with those computed by multidimensional numerical models. The observed and modeled deposition rates typically agree to within 20%. This agreement in energy deposition rates implies the same agreement exists between measured and modeled ozone volume mixing ratios in the mesosphere. Only in the upper mesosphere at midlatitudes during winter do we derive energy deposition rates (and hence ozone mixing ratios) consistently and significantly larger than the model calculations. This result is contrary to previous studies that have shown a large model deficit in the ozone abundance throughout the mesosphere. The climatology of solar energy deposition and heating presented in this paper is available to the community at the Middle Atmosphere Energy Budget Project web site at http://heat.budget.gats.inc.com.

Water-vapor mixing-ratio measurements in the solar-blind region

It is shown that, under clear sky conditions, water-vapor mixing-ratio measurements by solar-blind Raman lidars can be improved if the differential transmissivity is calculated by use of a single Raman signal instead of the usual Raman differential absorption lidar method, which allows one to exploit the large absorption cross section of ozone in this spectral region. We present a discussion of statistical and systematic errors in both methods and show the results of a numerical simulation.

Sensitivity of surface UV radiation and ozone column retrieval to ozone and temperature profiles

This paper discusses the influence of ozone and temperature profiles on surface UV radiation, and on total ozone column derived from global irradiance measurements. Measured ozone and temperature profiles from Legionowo, Poland, are used together with typical surface and cloudless atmosphere conditions. The effects of assuming a U.S. standard profile with scaled ozone column instead of actual profiles are analyzed. Variable temperature/ozone vertical distributions and different sets of ozone absorption cross section data may change erythemally weighted radiation by as much as 14% with respect to reference conditions. The mean and standard deviations of errors were generally below 2% but increased another 2–3% for large solar zenith angles. Uncertainties of up to 10% may be caused by using an inappropriate profile in total ozone column retrieval. We analyzed the underlying processes causing the uncertainties by selecting three ozone and temperature profile pairs characterized by the same unsealed total ozone amount but with different vertical distributions. Results obtained for cases with ozone redistribution from the stratosphere to the troposphere are consistent with earlier work. However, if the temperature profiles differ significantly in the stratosphere, an ozone redistribution may lead to a strong decrease in UV doses for high solar zenith angles. It is also shown that differences in ozone maximum height as well as in ozone concentration in the upper troposphere have a significant influence on surface UV radiation.

A new perspective on the molecular oxygen and hydroxyl airglow emissions

The mesospheric molecular oxygen and hydroxyl airglow emissions have traditionally been measured in order to derive minor species abundances or to diagnose dynamical phenomena. We present a new interpretation of these airglow emissions and show them to be fundamental measures of energy deposition from which rates of atmospheric heating are readily derived. The heating rate due to absorption of ultraviolet radiation in the Hartley band of ozone may be derived from simultaneous measurements of the oxygen atmospheric band and infrared atmospheric band volume emission rates independent of knowledge of the ozone density, the solar irradiance, and the ozone absorption cross sections. The heating rates due to key exothermic reactions may be derived directly from appropriate airglow observations independent of the reactant concentrations and the temperature‐dependent reaction rates. The accuracy of heating rates derived directly from airglow measurements is also inherently higher than that obtained in standard approaches. We suggest that heating rates derived in this manner be treated as data products and that they be compared with numerical model computations to enhance understanding of atmospheric thermodynamics. An initial comparison of airglow‐derived energy deposition rates with deposition rates traditionally computed from numerical models shows agreement to within 20% for the Hartley band of ozone in the lower and upper mesosphere.

Evidence for increasing ultraviolet irradiance at Point Barrow, Alaska

This paper presents analysis of noontime ultraviolet irradiance measurements made at Point Barrow, Alaska (71.2° N, 159° W) between the years 1991 and 1996. Eighteen wavelengths of the solar irradiance spectrum between 290 nm and 340 nm were examined for multiyear trends. This spectral region is particularly critical as these wavelengths are known to cause biological damage. After reducing the effects of clouds, 305 nanometer wavelength increases ranging between 3 and 10% per year were found in all daylit months except June which exhibited an annual average decline of approximately −3% per year at this wavelength. The correlation between the absorption cross‐section of ozone and the spectral character of the UV‐B changes suggest that declines in column ozone are responsible for the dramatic 305 nm increases. The unexpected decline in June 305 nm irradiance may be due to an increase in column ozone over this location in June.

Absorption Spectra Measurements for the Ozone Molecule in the 350-830 nm Region

Absolute absorption cross-sections of ozone have been measured at ambient (295 K) and low temperature (218 K) in the visible region corresponding to the Chappuis bands. The temperature effect has been studied and found to be very small. The minimum of the absorption between the Hartley and the Chappuis bands is observed for the first time at 377,5 nm.

Measurements of spectral solar UV irradiance in tropical‐Australia

Measurements of global spectral irradiance in the UV and visible range were carried out during December 1995 and January 1996 in Townsville, Australia (19.33°S, 146.76°E, 30 m above sea level (asl)) using the mobile spectroradiometer of the Fraunhofer Institute for Atmospheric Environmental Research, Germany. These are, to our knowledge, the first reported spectral UV measurements in the tropics of Australia. For cloudless days, the spectral measurements are consistent with results of a radiative transfer model. In the UVA, measurement and model agree within ±10% for solar elevations above 10°. In the UVB, the differences are larger (≈15% at 300 nm), which can be explained by uncertainties in the model input parameters of total ozone column and ozone absorption cross section. The variation of the daily erythemal irradiation was found to be ±24% (±1 σ) for the period of the campaign. The variation of the total ozone column contributes less than ±3% to this variability; the main part is introduced by clouds. These attenuate UV irradiation less than total irradiation (300 nm – 3000 nm); the daily total irradiation averaged over the period of the campaign was reduced by a factor of 0.71 owing to cloudiness compared to the clear‐sky case while the erythemal irradiation was only diminished by a factor of 0.78. Using long‐term records of total irradiation and ozone column, the parameters influencing UV radiation on Earth were found to be typical for the period and site of the campaign. The maximum erythemally weighted irradiance measured during the campaign was 429 mW/m2, and the average daily erythemal irradiation for this period was 6.06 kJ/m2. These high radiation levels were found to exceed the corresponding values for Garmisch‐Partenkirchen (47.5°N, 11.0°E, 730 m asl), Germany, by between 55 and 70%. This pronounced difference in the radiation environment between Australia and Germany is explained by the higher solar elevation and the lower ozone column in the tropics.

Transmittance of a cloud is wavelength‐dependent in the UV‐range: Physical interpretation

In the recently published GRL paper by Seckmeyer et al. [1996] an example of a cloud that has a wavelength dependent effect on the surface UV‐radiation is given. Through careful and accurate radiative transfer modelling, the present paper aims to give a physical interpretation of the reported wavelength dependence of this particular cloud. The modelling shows that the transmission of the cloud alone does not vary significantly with wavelength in the UV. However, the cloud gives a wavelength dependent effect in the surface UV‐radiation due to radiation scattered upwards from the cloud and then scattered downwards again, effectively trying to make it through the cloud more than once. The number of photons this happens to is a function of the wavelength dependent Rayleigh scattering and ozone absorption cross sections.