Final Report: Effects of Clouds and Tropospheric Air Quality on Surface UV at 6 UV Research Sites

EPA Grant Number: R833224
Title: Effects of Clouds and Tropospheric Air Quality on Surface UV at 6 UV Research Sites
Investigators: Lantz, Kathleen O. , Kiedron, Peter , Petropavlovskikh, Irina
Institution: Cooperative Institute for Research in Environmental Sciences
EPA Project Officer: Chung, Serena
Project Period: October 1, 2006 through September 30, 2010
Project Amount: $299,988
RFA: Implications of Tropospheric Air Pollution for Surface UV Exposures (2005) RFA Text |  Recipients Lists
Research Category: Global Climate Change , Air Quality and Air Toxics , Climate Change , Air


Locations across the continental United States will be used to evaluate the impacts of tropospheric air quality on surface UV irradiance measurements. These six sites are the re-established EPA UV Network and include Table Mountain near Boulder, CO, Rocky Mountain Research Station at Niwot Ridge, CO, Bondville, IL, Fort Peck, MT, Raleigh, NC, and Houston, TX. Our goals will be to evaluate UV-B irradiance from the six locations under a variety of atmospheric conditions.

The specific goals include (1) developing and implementing QA/QC procedures on the UV measurements and ancillary data. Procedures include comparing solar irradiance from the Brewer spectrophotometer to measurements from other co-located instruments (i.e. UV broadband radiometers and UV filter radiometers). (2) An algorithm will be developed for determining ozone profiles from Brewer Umkehr measurements and inferring tropospheric ozone column. (3) Cloud and aerosol properties will be collected from a suite of co-located instruments as part of the SURFRAD Network within the Surface Radiation Research Branch (SRRB), Earth System Research Laboratory, NOAA, and the USDA UV monitoring program. (4) Using the direct-to-diffuse ratio from the UV-MFRSR combined with a UV radiative transfer code, the aerosol single scattering albedo will be estimated for clear-sky conditions at the six sites. (5) The atmospheric conditions will be characterized for total ozone, cloud properties, and atmospheric pollutants. (6) We will provide a comprehensive evaluation of the impact of total ozone, cloud cover, and air quality on the tropospheric UV-B transmission. The database provided by the Central UV Calibration Facility, the Surface Radiation and Research Branch of ESRL/NOAA, and the USDA UV Monitoring Program will provide a unique and valuable data-set that will help identify the impacts of variable conditions of cloud cover and tropospheric air quality on UV irradiances.

Summary/Accomplishments (Outputs/Outcomes):

This document provides a summary of results of the EPA STAR funded proposal “Effects of Clouds and Tropospheric Pollution on Surface UV at six EPA UV Research Sites”. This project worked to provide high quality UV spectral solar irradiance, erythema (UV Index), ozone profiles, and tropopsheric ozone column. The project’s focus is provide the high quality products to study changes in surface UV levels caused by atmospheric pollutants, including aerosols and tropospheric ozone, and clouds. The re-established NOAA/EPA UV Network at six locations across the United States is currently measuring UV radiation and automated direct sun and zenith sky ozone measurements from which daily ozone profiles can be derived. A summary of activities is given below.

Spectral UV Solar Irradiance and Erythema (UV Index):

Stray-light and spike removal corrections to UV solar irradiance measurements: Several diagnostic plots of Brewer spectrophotometer measurements were made available on the NEUBrew web-site. Level 101 UV solar irradiance and erythema data were corrected for dark counts and dead time. Procedures were developed and implemented for generating higher-level spectral solar irradiance and erythema (level 201) both as web generated graphs and ftp ascii files. Both files and plots are available from the NEUBrew web-site, The corrections include spike detection and spike removal algorithms [Kiedron et al., May 2008] and stray light correction [Kiedron et al., June, 2008]. Level 201 spectral solar irradiance is used to generate UV dose and erythema according to algorithms outlined in Kiedron et al., December 2007. General information on NEUBrew and new products was presented at the Quadrennial Ozone Symposium, Tromso, Norway [Disterhoft et al., 2008].

Temperature corrections to UV solar irradiance measurements: The Brewer spectrophotometers were originally designed for total ozone measurements. For the ozone measurements the count rates are corrected for the temperature dependent band-pass of the various filters and components inside the assembly, and therefore the instruments are not typically temperature stabilized. Because total ozone calculations rely on ratios, the temperature dependence is not as critical as long as the temperature dependence is wavelength independent. However this is not the case for UV solar irradiance measurements where temperature changes can cause a significant error in the solar irradiance measurements. The instrument is not temperature stabilized but is heated giving internal temperatures typically between 0 and 40 deg Celsius for the NEUBrew sites. Given temperature changes of 40 deg, responsivities and hence solar irradiance can change as much as 20% for the instruments in NEUBrew. The percent change per degree in the responsivities of the Brewer spectrophotometer was investigated previously by Weatherhead et al, 2001 and was found to be instrument dependent. Several Brewer spectrophotometers used in the previous study are part of the NEUBrew network, however two instruments were not part of the earlier study, i.e. Houston, TX and Raleigh, NC. The question arises as to whether the temperature coefficients have changed from the earlier work as well as the need to generate temperature coefficients for the two additional instruments. We generated spectral temperature coefficients using external lamp measurements and using internal lamp measurements. Temperature coefficients developed here were comparable to the previous studies within the uncertainties giving confidence to the temperature coefficients. Procedures were developed and implemented for generating higher-level spectral solar irradiance that is temperature corrected (level 211) both as web generated graphs and ftp ascii files. Both files and plots are available from the NEUBrew web-site, A document describing the determination of the temperature coefficients and how they are applied to the data is available under the documents link on the NEUBrew web-site [Lantz et al., 2009a]. These results were presented at the 12th Biennial WMO-GAW Brewer Users Group Meeting, Aosta, Italy, September 20 – 26, 2009 and a summary was given in the Workshop WMO Report [Lantz et al., 2009].

Angular Response Corrections to UV Solar Irradiance and Erythema: Procedures were developed to correct Brewer UV spectral solar irradiance measurements for the angular error. The angular correction routine was developed in two ways: 1) Uses a look-up table of diffuse-to-dirrect solar irradiance ratios (DDR) from RT calculations incorporating laboratory measurements of the direct cosine error of each instrument to compute an angular response correction. 2) Developed a methodology to use the direct-to-diffuse irradiance ratio (DDR) from co-located UV-MFRSR measurements and uses an isotropic assumption for overcast days and a radiative transfer model radiance distribution for clear skies with and without aerosols. Level 212 UV solar irradiance data that is corrected for angular response errors was generated and made available on NEUBrew web-site (Figure 1). Also, a document describing the angular response corrections to the Brewer solar irradiance measurements are available from the NEUBrew web-site [Lantz et al., 2009b]. These results were presented at the “Conference on 100 Years of UV Measurements at PMOD, Davos, Switzerland, September 18 – 20, 2007 [Lantz et al., 2007].

Figure 1. Example of Level 212 UV Spectral solar irradiance from Brewer Spectrophotometer located at Table Mountain Test Facility from NEUBrew web-site.

Comparisons of Brewer UV Index to NWS UV Index Forecasts: The NEUBREW network (NOAA-EPA UV Network) was designed to investigate factors affecting surface UV solar irradiance. UV index from the Brewer spectrophotometers for the six sites are compared to the NCEP UV forecast and plots are available next day on the NEUBrew web-site. Early results indicate that at the “dirtier” sites the UV forecast is high with respect to the measurements. However, this needs to be re-evaluated after further QA/QC levels of the Brewer data have been generated. The UV forecast considers forecasted ozone and clouds, ground albedo, surface elevation, and aerosol properties for the calculations. The discrepancies set the stage for evaluating measured parameters representing air quality and clouds on solar uv radation at the sites. Calculations of erythemally weighted solar irradiance and the UV Index from Brewer UV spectral solar irradiance measurements is described in Kiedron et al., 2007. Figure 2 gives an example of the comparison of the 5-day NOAA/NCEP 5-day forecast to the Brewer measurements of UV Index for the six NEUBrew sites.

Figure 2. Example of Brewer UV Index measurements compared to NOAA/NCEP/CPC UV Index 5-day forecast for 6 NEUBrew sites available on the NEUBrew web-site.

Erythema and UV Index Calibration Verification: In addition to erythema and UV index from the Brewer spectrophotometer at each of the sites, erythema and UV index can be derived from the co-located UV broadband radiometer. Solar zenith angle dependent erythema calibration factors were applied to the UV broadband radiometers to calculate an erythemally weighted solar irradiance. The comparison between the two instruments has been made available on the NEUBrew web-site ( The accuracy of the calibration of the broadband radiometers for erythema used for this work was verified in an intercomparison between international UV calibration facilities [Hulsen et al., 2008]. Results indicated a difference of 0.2% at high sun from the Physikalisch-Meteorologisches Observatorium (PMOD) calibration reference in Davos, Switzerland.

UV variability due to total ozone and tropospheric ozone: Level 211 UV solar irradiance from the Brewer spectrophotometers was investigated against total ozone and tropospheric ozone for the six sites. Tropospheric ozone determined from the Umkehr ozone profiles of the Brewer spectrophotometers and level 200 total ozone from the Brewer spectrophotometer was used in the analysis. Total ozone and tropospheric ozone column derived from the Brewer spectrophotometers was used as inputs to the TUV radiative transfer. Results for the initial analysis of measured UV solar irradiance versus tropospheric ozone was inconclusive and statistically insignificant. However, the temperature dependence of the Brewer spectrophotometer measurements could likely mask the effect. We would like to repeat this study using the Level 212 temperature-corrected UV solar irradiance measurements.

UV Actinic Flux and Brewer ozone profiles: The Tropospheric UV and Visible Radiative Transfer Model (TUV) is used to evaluate the impact of measured ozone profiles on UV photolysis rate coefficients in the troposphere compared to the default U.S. Standard atmosphere ozone profile often used in photochemical models. The measured ozone profiles used in the RT calculations of photolysis rate coefficients are from three sources: 1) Ozonesondes from the Earth System Research Laboratory of NOAA during the summer and fall of 2000; 2) Brewer Umkehr retrievals from the NOAA-EPA Brewer spectrophotometer Network (NEUBrew) during the winter, spring, summer, fall of 2007; and 3) ozonesondes from Valparaiso University during IONS and INTEX-B campaigns in the summer of 2004 and spring/summer 2006. The radiative transfer calculations are performed from the surface to 12 km. In addition, sensitivity studies are performed for the effect of redistribution of ozone to the lower troposphere and for a shift in the altitude position of the ozone peak on UV solar radiation. The effect of changes in the ozone profile from the standard ozone profile has very little effect on j(NO2) as expected. Larger effects are seen in shorter wavelengths of actinic flux and in j(O3) and at larger solar zenith angles. Usage of the standard ozone profile in computations of ozone photolysis rate coefficients will slightly underestimate by 1-2% the photolysis rate coefficients for small surface ozone amounts and will overestimate the surface photolysis rate coefficient by 2-8% for larger amounts of surface ozone. In the vertical, the standard ozone profile has the ozonepause 5 km lower than observations for the Houston area. As a result, usage of the standard profile will increasingly underestimate the ozone photolysis rate coefficient by approximately 0-10%. Changes in j(O3) will affect the concentration of the hydroxyl radical in the atmosphere and therefore can affect the oxidative capacity of the atmosphere. Results were presented at the Fall AGU Conference 2010 [Lantz et al., 2010] and a paper is in preparation [Lantz et al., 2011].

UV Index and Clouds: A smart-phone application proto-type was been developed for calculating time to sunburn and estimating solar vitamin D production. Cumulative and over-exposure to UV solar irradiance plays a significant role in many types of skin cancer, but is necessary for the production of vitamin D, whether in plants or in human skin. The smart phone application (“app”) is a tool for avoiding a sun-burn (erythema) while tracking human vitamin D production during outdoor activities. As part of this activity, we evaluated cloud fraction on UV Index. This exercise compared observer estimated cloud fraction with cloud fraction measured by the Total Sky Imager (TSI). The observer-based cloud fraction was conducted at Table Mountain Test Facility using 10-15 volunteers in 3 time periods per day over three days with varying cloud cover. Cloud fraction from both the observers and the TSI were applied to a clear-sky UV forecast and compared to ground-based measurements from the Brewer Spectrophotometer. The results were presented at the GMD Annual Meeting, 2010 [Lantz et al., 2010] and will be published in a future publication [Lantz et al., 2011].

Aerosol properties and UV surface albedo:

Aerosol properties with the UV-RSS: The first successful deployment of the fully- operational ultraviolet rotating shadow-band spectroradiometer occurred during the May 2003 US Department of Energy’s Atmospheric Radiation Measurement program’s Aerosol Intensive Observation Period. The Atmospheric Radiation Program (ARM) site is located in northern Oklahoma. The aerosol properties in the visible range were characterized using redundant measurements with several instruments to determine the column aerosol optical depth, the single scattering albedo, and the asymmetry parameter needed as input for radiative transfer calculations of the downwelling direct normal and diffuse horizontal solar irradiance in clear-sky conditions. The Tropospheric Ultraviolet and Visible (TUV) radiative transfer model was used for the calculations of the spectral irradiance between 300–360 nm. Since there are few ultraviolet measurements of aerosol properties, most of the input aerosol data for the radiative transfer model are based on the assumption that UV input parameters can be extrapolated from the visible portion of the spectrum. Disagreements among available extraterrestrial spectra, which are discussed briefly, suggested that instead of comparing irradiances, measured and modeled spectral transmittances between 300–360 nm should be compared for the seven cases studied. Transmittance was calculated by taking the ratios of the measured irradiances to the Langley-derived, top-of-the-atmosphere irradiances. The cases studied included low to moderate aerosol loads and low to high solar-zenith angles. A procedure for retrieving single scattering albedo in the ultraviolet based on the comparisons of direct and diffuse transmittance is outlined. The strength of this method is in using transmittances to avoid uncertainties in the extraterrestrial fluxes and by first fitting the direct and diffuse transmittance separately, the accuracy of the aerosol optical depth can be verified. For this study, five days in the spring of 2003 were used to evaluate the method. The retrieved UV single scattering albedo for this location are typically lower by 0.03 to 0.1 from the SSA at 550 nm, except in one case where the SSA was higher by 0.015. Specifics of the results of this work are described in Michalsky and Kiedron [2008].

Aerosol properties from UV-MFRSR: For our studies of air quality on UV radiation, aerosol optical properties are required which include aerosol optical depth and aerosol single scattering albedo. Direct-to-diffuse solar irradiance ratios (DDR) from a co-located UV Rotating Shadowband Spectrograph (UV-RSS) and a UV-MFRSR were compared as part of the development of an algorithm for the calculation of aerosol single scattering albedo. Sensitivity studies were conducted of the DDR to several atmospheric parameters (i.e. AOD, aerosol single scattering albedo, asymmetry parameter, ground albedo, and tropospheric and stratospheric O3 and NO2) using the TUV radiative transfer model. The sensitivity studies provide guidelines on the uncertainty of the input parameters to the DDR and derived aerosol single scattering albedo. For the NEUBrew network, single scattering albedo was calculated for the Table Mountain test facility site (TMTF). Each of the six NEUBrew sites has a UV Multi Filter Shadowband Radiometer (UV-MFRSR), but the TMTF site also has a collocated UV rotating shadowband spectrograph (UV-RSS) that provides diffuse and direct spectral UV solar irradiance from 300 – 360 nm with a spectral resolution that varies between 0.25 and 0.45 nm. Inputs to the SSA retrieval algorithm included aerosol properties in the UV and/or extrapolated from visible measurements (i.e. aerosol optical depth, Angstrom coefficient, asymmetry parameter), surface albedo, total ozone, and ozone profiles. Information was obtained from instrumentation and products from NEUBREW, SURFRAD, USDA UV monitoring program, and AERONET. Direct-to-diffuse solar irradiance ratios (DDR) from a co-located UV Rotating Shadowband Spectrograph (UV-RSS) and a UV-MFRSR have been compared further as part of the development of an algorithm for the calculation of aerosol single scattering albedo (w0). Initial results indicate good agreement between the two instruments at high sun for the channels from 305 – 368 nm. However, discrepancies in DDR at low sun (70°) are as much as 10% for specific channels. The discrepancies appear to follow the angular response errors of the UV-MFRSR channels and indicate that the angular response corrections to the signals may need to be re-evaluated an improved. A change in DDR of 0.05 gives an error of approximately 0.06 in w0 when the aerosol optical depth is 0.2. Results gave a single scattering albedo from 0.84 to 0.91 for the UV spectral range for a limited set of data. Results were presented at the American Geophysical Union, Fall Meeting, 2008 [Lantz et al., AGU, Fall 2008].

UV Surface Albedo: Accurate measurements of the surface albedo are necessary for the retrievals of aerosol single scattering albedo and for studying factors affecting surface UV solar irradiance. In March 2008, a tower was installed at the Table Mountain Test Facility to measure surface albedo in the UV and the visible. The tower is approximately 25 feet tall with two 3 feet extensions perpendicular to the tower that hold the downward viewing vis-MFRSR and a broadband radiometer for measuring up-welling solar radiation. On the TMTF deck there is a vis-MFRSR and a UV broadband radiometer to measure downwelling solar radiation (i.e. 415 – 868 nm and erthemally-weighted solar irradiance, respectively). The four instruments were calibrated prior to installing the tower with the radiometers. Calibrations of the UV instruments are scheduled once per year. In addition, spectral UV surface albedo measurements were made with a UV-MFRSR and a UV broadband radiometer on a short-term basis with the up-welling measuring instruments maintained at an 8 ft height. The short-term measurements were compared to the tower measurements and were in good agreement for this site. The spectral UV surface albedo measurement gave a surface albedo of 1.7% to 3.1% from 305-nm to 368-nm.

Total Ozone, Tropopsheric Ozone, and Ozone profiles:

Tropopsheric ozone: The variability in tropopsheric ozone comes from hydrocarbons from plants, transport from the stratosphere, pollution, UV sunlight initiated chemistry etc. The reason we monitor tropospheric ozone is that it is harmful to humans and the environment, and it is considered as a greenhouse gas. The tropopsheric ozone product is used to access how it modulates UV solar radiation as described in the next section.

This work evaluated the quality of tropospheric ozone information derived from the ground-based Brewer zenith sky measurements. Monitoring of the day-to-day and diurnal tropospheric ozone changes is one of the science objectives of this grant. Tropospheric ozone data was evaluated through comparisons with co-incident ozonesonde measurements of high vertical resolution. Figure 4 gives tropospheric ozone column from the Umkehr ozone profile retrievals. The analysis concentrated on the short-term and long-term tropospheric ozone variability detected by co-incident and co-located Brewer data along with ozone profiles from ozone-sondes available from Boulder, CO. The studies of the day-to-day variability in the tropospheric ozone suggest that no more than 1-day separation is allowed between the ozone-sonde launch and Brewer Umkehr measurement. It appears to be especially important in the winter and spring time period of measurements in Boulder area, when there is a high frequency of high-latitude air-mass intrusions in the middle latitudes. Never-the-less, analyses suggest that Umkehr technique performed by the well-calibrated Brewer is capable of monitoring short-term variability in tropospheric ozone. We also filter data using: meteorological regimes, tropopause heights/troposphere thicknesses and back trajectories.

The same day ozone-sonde and Umkehr data in Boulder between 1978 and 2007 provide correlation of 52%, and the slope of the scatter plot is ~ 0.56. Comparisons of Umkehr data taken one day apart are investigated where the correlation is found to be as low as 34%. The reason for the low correlation is high variability in the tropopsheric ozone due to transport and local pollution sources. Our best possiblity is then to see comparisons as good as this situation. Following the method Follette-Cook, we find that the correlation can be improved from 17 to 36 % when measurements are taken on different days but are in the same meteorological regime (defined by location of subtropical and polar jets) [Petropavlovskikh et al., 2006; Petropavlovskikh et al., 2007; Petropavlovskikh et al., Ozone Symposium, 2008].

Figure 4: Example of tropospheric ozone column derived from Brewer ozone profiles for Table Mountain Test Facility, Boulder, CO. These figures are available for the NEUBrew sites on the web-site.

Total Ozone: Ozone column data is generated using internal Brewer spectrophotometer procedures from direct sun (DS) observations. Average daily total ozone values are obtained from measurements with air masses less than four and for cases when the standard deviation of five individual measurements constituting the DS procedure is less than 2.5 DU. From here, level 200 ozone column data are generated and are corrected for the throughput instability. Level 200 data is implemented because the effective extraterrestrial constant is affected by instrument throughput -where in the case of the MKIV Brewer spectrophotometer is chiefly sensitive to the solar blind filter that is made of hygroscopic NiSO4 crystal. The correction uses two or more daily internal quartz tungsten halogen lamp measurements. The level 200 ozone column significantly improved correlation with OMI data for the few Brewers that experienced drift due to solar blind filter instability. In particular we obtained encouraging results with Brewer #139 that had the NiSO4 filter altogether replaced with Schott UG11 color glass filter. This result gives us confidence that the expensive NiSO4 filter is not always necessary, and in the future it might be replaced with a UG11 filter. The level 200 data ozone column data are available as web graphs and the ftp ascii text files will be released shortly.

Stray light errors in the ozone column data from MKIV Brewer spectrophotometers were evaluated and a limit for maximal slant path column was established to be about 1200 DU [Kiedron et al., June, 2008]. The possibility of a different mathematical algorithm for ozone retrieval was investigated that could partially correct the stray light error. This algorithm has not been implemented in routine calculations.

Ozone retrievals are dependent on ozone profiles (particularly for large air masses) and on the effective profile temperature. Using UV-RSS Table Mountain data we explored the possibility of detecting the effective ozone profile temperature. These results were presented at the Ozone symposium [Kiedron and Michalsky, Ozone Symposium, 2008].

Total Ozone from the Brewer spectrophotometer and Ozone Monitoring Instrument (OMI) aboard the AURA satellite: Brewer total ozone (Level 1) is routinely compared to OMI total ozone with plots available on the web-site. An example of the omparisons of OMI and Brewer Total Ozone for the Boulder, CO NEUBrew site are given in Figure 5.

For improvements in measurements of total ozone, a Langley regression based method was explored to monitor the extraterrestrial constant (ETC) that would be independent of measurements with the internal lamp. This method could effectively reduce the frequency for external Brewer calibrations such as the one performed by Environment Canada. At the Biennial Brewer’s meeting, Peter Kiedron presented and gave an overview of the use of Langley regression method for improving total ozone measurements within the NEUBrew Network [Kiedron et al., 2009]. Equations were presented for the correction of the total ozone measurements using the Langley derived correction to the ETC. Issues included non-constant aerosols and pressure. Three data levels of total ozone were calculated and are given in figure 2: Level 101 uses ETC from calibration, Level 200 uses ETC from Brewer R6 measurements, and Level 300 uses ETC from Langley regressions. Level 300 total ozone data is available from the NEUBrew web-page.

Figure 5: Example of Total Ozone from the Brewer Spectrphotometer for Table Mountain Test Facility, Boulder, CO compared to the OMI satellite measurements. These figures are available for the 6 NEUBrew sites on the web-site.

Ozone profiles and algorithm development. One of the goals of the three-year project is to improve the quality of ozone profiles retrieved from the Brewer Umkehr measurements and to infer an improved tropospheric ozone column. In accordance with the project objectives, a working version of the Brewer Umkehr ozone profile retrieval algorithm was developed. Umkehr measurements are performed by the Brewer spectrophotometer during sunrise and sunset elevations for solar zenith angles between 70 to 90 degrees. Eight specific wavelengths are scanned, i.e. 306 nm, 310 nm, 313 nm, 317 nm, 319 nm, 323 nm, 326 nm, and 329 nm. The photon counts are converted to the log of the zenith-sky radiances and are plotted as a function of solar zenith angle for both morning and afternoon measurements. These automated plots are available and viewed daily for quality control checks at the NEUBrew web page at Using the improved algorithm, vertical ozone profiles are routinely derived from Umkehr scans and subsequently uploaded to the NEUBrew web-pages. High and poor quality retrieved profiles have the sub-title text colored in green and red respectively. Retrievals are considered of high quality if their iterations are less than four, and final residuals of the retrieval are less than one. An example of an ozone profile retrieved from Brewer Umkehr measurements for Table Mountain Test Facility, Boulder, CO is given in figure 3.

This project investigated several issues to improve the ozone profile measurements and hence the tropospheric ozone product. Each instrument in the NEUBrew network has specific spectral settings that were measured at the calibration facility in Boulder, CO. Parameters such as each channels’ wavelength settings, band-pass profile, filter polarization characteristics, and out-of-band signal were assessed for several instruments located at the Table Mountain Site, Boulder, CO. The ozone profile retrieval algorithm (originally developed for the Dobson Umkehr was optimized by incorporating information specific to optical and spectro-radiometric characteristics of each Brewer Mark IV instrument in the NEUBrew network.

In addition, cloud interference in the automated Brewer Umkehr measurements was addressed. To assure quality of the Brewer ozone profile retrievals, zenith sky radiation measurements are screened for interference of clouds in the zenith angle view. Details of the improvements can be found in previous EPA Star Grant annual reports, as well as in several conference presentations and published papers [Flynn et al., AGU, Fall 2008; Petropavlovskikh et al., 2005a; Petropavlovskikh et al. 2005b; Petropavlovskikh et al., 2009; Petropavlovskikh et al., Ozone Symposium, 2008]. The improvement of the Brewer ozone profile retrieval algorithm has continued in the last year of the project. Results of the research have been presented at the WMO ozone cross section meeting in Geneva in May 2009 [Petropavlovskikh et al., 2009a] and at 12th Biennial WMO-GAW Brewer Users Group Meeting at Aosta, Italy, 20-26 September 2009 [Petropavlovskikh et al., 2009b].

The Brewer Umkehr retrieval algorithm was assessed for sensitivity to effects of changes in ozone cross-section, stray light correction, and the atmospheric temperature variability. The matching of the retrieved ozone profile to the measured Umkehr curve is based on the radiative transfer model (or forward model) that is designed to simulate the zenith sky radiance at the surface under conditions matching those during observations. The spectrally resolved radiance is calculated as downward UV radiation emitted by the Sun from the nominal SZA. From this, the amount of radiation attenuated by molecular scattering and ozone absorption under similar climatological conditions is used as the first guess. The ozone absorption coefficients and their sensitivity to temperature (second degree polynomial fit) are determined from laboratory measurements by Bass and Paur or Daumont. Since zenith sky radiation measured by the Brewer is integrated over the band-pass, accurate knowledge of the band-pass spectral shape and position are important for the simulation of zenith-sky conditions. The research addresses the effect of the uncertainties in the ozone absorption spectrum and its temperature dependence on results of the forward model simulations for Brewer Umkehr measurements, and thus their retrieved ozone profile. Research studies were recently submitted for publication [Petropavlovskikh et al., 2010]. I. Petropavlovskikh attended two ASCO Meetings ("Absorption Cross Sections of Ozone"). This committee established 
in the spring 2009 is a joint ad hoc commission of the Scientific Advisory 
Group (SAG) of the Global Atmosphere Watch (GAW) of the World Meteorological Organization (WMO) and the International Ozone Commission 
IO3C) of the International Association of Meteorology and Atmospheric 
Sciences (IAMAS).

Figure 3: Example of ozone profiles derived from Brewer Umkehr measurements at Table Mountain Test Facility, Boulder, CO. These figures are available for the NEUBrew sites on the web-site.

Journal Articles on this Report : 6 Displayed | Download in RIS Format

Other project views: All 35 publications 13 publications in selected types All 6 journal articles
Type Citation Project Document Sources
Journal Article Hulsen G, Grobner J, Bais A, Blumthaler M, Disterhoft P, Johnsen B, Lantz KO, Meleti C, Schreder J, Vilaplana Guerrero JM, Ylianttila L. Intercomparison of erythemal broadband radiometers calibrated by seven UV calibration facilities in Europe and the USA. Atmospheric Chemistry and Physics 2008;8(16):4865-4875. R833224 (2008)
R833224 (Final)
  • Full-text: ACP-Full Text PDF
  • Abstract: ACP-Abstract
  • Journal Article Michalsky JJ, Kiedron PW. Comparison of UV-RSS spectral measurements and TUV model runs for clear skies for the May 2003 ARM aerosol intensive observation period. Atmospheric Chemistry and Physics 2008;8(6):1813-1821. R833224 (2008)
    R833224 (Final)
  • Full-text: ACP-Full Text PDF
  • Abstract: ACP-Abstract
  • Journal Article Petropavlovskikh I, Bhartia PK, DeLuisi J. New Umkehr ozone profile retrieval algorithm optimized for climatological studies. Geophysical Research Letters 2005;32(16):L16808 (5 pp.). R833224 (Final)
  • Full-text: AGU-Fulll Text HTML
  • Other: AGU-Full Text PDF
  • Journal Article Petropavlovskikh I, Ahn C, Bhartia PK, Flynn LE. Comparison and covalidation of ozone anomalies and variability observed in SBUV(/2) and Umkehr northern midlatitude ozone profile estimates. Geophysical Research Letters 2005;32(6):L06805 (5 pp.). R833224 (Final)
  • Full-text: AGU-Full Text HTML
  • Other: AGU-Full Text PDF
  • Journal Article Petropavlovskikh I, Evans R, McConville G, Miyagawa K, Oltmans S. Effect of the out-of-band stray light on the retrieval of the Umkehr Dobson ozone profiles. International Journal of Remote Sensing 2009;30(24):6461-6482. R833224 (2009)
    R833224 (Final)
  • Full-text: ResearchGate-Full Text PDF
  • Abstract: Taylor and Francis-Abstract
  • Journal Article Petropavlovskikh I, Evans R, McConville G, Oltmans S, Quincy D, Lantz K, Disterhoft P, Stanek M, Flynn L. Sensitivity of Dobson and Brewer Umkehr ozone profile retrievals to ozone cross-sections and stray light effects. Atmospheric Measurement Techniques 2011;4(9):1841-1853. R833224 (Final)
  • Full-text: AMT-Full Text PDF
  • Abstract: AMT-Abstract
  • Supplemental Keywords:

    Stratospheric Ozone, Tropospheric Ozone, Air Quality, Aerosol Optical Depth, Cloud Properties, Multi-Filter Rotating Shadowband Radiometer, TSI Sky Imager, Brewer Spectroradiometer, Ultraviolet, TUV Radiative Transfer Model, DISORT,, RFA, Air, climate change, Air Pollution Effects, Atmosphere

    Relevant Websites: 

    Progress and Final Reports:

    Original Abstract
  • 2007 Progress Report
  • 2008 Progress Report
  • 2009 Progress Report