Validation of Ozone Monitoring Instrument UV Satellite Data Using Spectral and Broadband Surface Based Measurements at a Queensland Site

This research reconstructed and validated the broadband UVA irradiances derived from discrete spectral irradiance data retrieved from the Ozone Monitoring Instrument (OMI) satellite from 1 January to 31 December 2009. OMI data at solar noon were compared to ground‐based spectral irradiances at Toowoomba (27°36′ S 151°55′ E), Australia, at 310, 324 and 380 nm for both cloud‐free and all sky conditions. There was a strong relationship between the ground‐based UV spectroradiometer data and satellite‐based measurements with an R² of 0.89 or better in each waveband for cloud‐free days. The data show an overestimate of the satellite‐derived spectral irradiances compared to the ground‐based data. The models developed for the subtropical site data account for this overestimation and are essential for any data correlation between satellite‐ and ground‐based measurements. Additionally, this research has compared solar noon broadband UVA irradiances evaluated with a model and the discrete satellite spectral irradiances for the solar noon values of cloud‐free days to those measured with a ground‐based UVA radiometer. An R² of 0.86 was obtained confirming that for cloud‐free days the broadband UVA can be evaluated from the OMI satellite spectral irradiances.     

Effect of cloud on UVA and exposure to humans

The daily autumn and winter ultraviolet-A (320-400 nm) (UVA) exposures and 6 min UVA irradiance data for a southern hemisphere subtropical site (Toowoomba, Australia, 27.6 degrees S, 151.9 degrees E) are presented. This data is used to quantify the effect of cloud on UVA using an integrated sky camera and radiation system. Additionally, an estimate of the effect of enhanced UVA exposure on humans is made. The measurement system consisted of broad-band visible-infrared and UVA sensors together with a sun tracking, wide-angle video camera. The mean daily June exposure was found to be 409 kJ m-2. Under the constraints of the uncertainty of both the UVA measurement system and clear-sky model, one case of enhanced UVA irradiance was found. Three cases of cloud enhancement of daily UVA exposure, approaching clear-sky levels, were also determined using a calculated clear-sky envelope. It was also determined that for a fulltime outdoor worker the additional UVA exposure could approach approximately that of one third of a full winter's day. For indoor workers with an outside lunch break of 12:00-1:00 P.M. the additional UVA exposure was on an average 6.9 kJ m-2 over three cloud-enhanced days. To the authors' knowledge this is the first paper to present some evidence of cloud-enhanced UVA human exposure.     

Lower body anatomical distribution of solar ultraviolet radiation on the human form in standing and sitting postures

Humans undertake their daily activities in a number of different postures. This paper aims to compare the anatomical distribution of the solar erythemal UV to human legs for standing and sitting postures. The exposure ratios to the legs (ratio of the UV exposure to a particular anatomical site compared to the ambient) have been measured with UV dosimeters for standing and sitting postures of a manikin. The exposure ratios for the legs ranged from 0 to 0.75 for the different anatomical sites for the sitting posture in summer (December through February) compared to 0.14 to 0.39 for the standing posture. In winter (June through August) the exposure ratios ranged from 0.01 to 0.91 for sitting to 0.17 to 0.81 for standing. For the anterior thigh and shin, the erythemal UV exposures increased by a factor of approximately 3 for sitting compared to standing postures. The exposure ratios to specific anatomical sites have been multiplied by the ambient erythemal UV exposures for each day to calculate the annual exposures. The annual erythemal exposures to the anterior thigh and ankle were predicted to be higher than 800 MED for humans sitting outdoors each day between noon and 13:00 h Australian Eastern Standard Time (EST). For humans standing outdoors during this time, the annual erythemal UV exposure averaged over each leg site was 436 MED, whereas, the averaged annual erythemal UV exposure was 512 MED for the sitting posture. Similarly, the annual erythemal UV exposure averaged over each of the sites was 173 MED for humans standing outdoors between 09:00 h EST and noon each Saturday morning and 205 MED for humans sitting outdoors during this time. These results show that there is increased risk of non-melanoma skin cancer and malignant melanoma to the lower body if no UV preventative strategies are employed while in a sitting posture compared to a standing posture.     

Plant Canopy Shape and the Influences on UV Exposures to the Canopy

The solar spectra at selected sites over hemispherical, conical and pinnacle plant canopy models has been evaluated with a dosimetric technique. The irradiance at the sites varies by up to a factor of 0.31 compared to the irradiance on a horizontal plane. The biologically effective (UVBE) exposures evaluated with the dosimetric technique at sites over the plant canopy are up to 19% of that on a horizontal plane. Compared to a spectroradiometer, the technique provides a more practicable method of measuring the UVBE exposures at multiple sites over a plant canopy. Usage of a dosimeter at one site to provide the exposures at that site for different sun angles introduces an error of more than 50%. Knowledge of the spectra allowed the UV and UVBE exposures to be calculated at each site along with the exposures to the entire canopies. These were dependent on the sun angle and the canopy shape. For plant damage, the UVBE was a maximum of about 1.4 mJ cm ² min^?1. Compared to the hemispherical canopy, the UVBE exposure for generalized plant damage was 45% less for the pinnacle canopy and 23% less for the conical canopy. The canopy exposures could not be determined from measurements of the ambient exposure.     

Intercomparison of Effective Erythemal Irradiance Measurements from Two Types of Broad-Band Instruments during June 1995

The biologically effective global solar ultraviolet radiation (UVR) measurements from a multiband UVR monitor and a conventional broadband UVR monitor are compared. The measurements were performed during the varied weather conditions of June 1995. We compared the daily total exposures measured by both instruments, as well as the ratio of the measured doses throughout the course of each day. The daily total exposures agreed within approximately 11% throughout the month. The ratio between the measured doses held at 1.12 between 0900 and 1700 h (solar zenith angles ?16-52°). The ratio decreased from 1.12 to 0.90 during the next 90 min outside that period (solar zenith angles ?52-72°) and decreased further beyond that point. Spectral response and cosine response mismatch between the instruments are discussed as the possible cause of discrepancies between the measured doses. Implications for erythemal irradiance monitoring and suggestions for further study are discussed.     

The Austrian UVA‐Network

The ultraviolet‐A (UVA) part of the solar spectrum at the Earth's surface is an essential environmental factor but continuous long‐time monitoring of UVA radiation is rarely done. In Austria, three existing stations of the UV monitoring network have been upgraded with UVA broadband instruments. At each station, one instrument measures global UVA irradiance and—in parallel—a second instrument measures diffuse irradiance. Recent and past measurements are available via a web page. This paper describes the used instruments, calibration and quality assurance and control procedures. Global and diffuse UVA measurements during a period of up to 5 years are presented. Data indicate clear annual courses and an increase of UVA with altitude by 8–9% per 1000 m. In the first half of the year, UVA radiation is higher than in the second half, due to less cloudiness. In Vienna (153 m asl), the mean daily global UVA radiant exposure in summer is almost as high as at Mt. Gerlitzen (1540 m asl), equalizing the altitude effect, due to less cloudiness. However, in winter, the UVA radiant exposure at Mt. Gerlitzen is double as high, as in Vienna.     

Minimum Exposure Limits and Measured Relationships Between the Vitamin D,Erythema and International Commission on Non‐Ionizing Radiation Protection Solar Ultraviolet

The International Commission on Non‐Ionizing Radiation Protection (ICNIRP) has established guidelines for exposure to ultraviolet radiation in outdoor occupational settings. Spectrally weighted ICNIRP ultraviolet exposures received by the skin or eye in an 8 h period are limited to 30 J m^?2. In this study, the time required to reach the ICNIRP exposure limit was measured daily in 10 min intervals upon a horizontal plane at a subtropical Australian latitude over a full year and compared with the effective Vitamin D dose received to one‐quarter of the available skin surface area for all six Fitzpatrick skin types. The comparison of measured solar ultraviolet exposures for the full range of sky conditions in the 2009 measurement period, including a major September continental dust event, show a clear relationship between the weighted ICNIRP and the effective vitamin D dose. Our results show that the horizontal plane ICNIRP ultraviolet exposure may be used under these conditions to provide minimum guidelines for the healthy moderation of vitamin D, scalable to each of the six Fitzpatrick skin types.     

UV exposure of elementary school children in five Japanese cities

A 1 week UV‐exposure measurement and outdoor‐activity pattern survey was conducted for elementary school children for four seasons at five sites in Japan, i.e. Sapporo (43°05′N, altitude 40 m), Tsukuba (36°05′N, 20 m), Tokyo (35°40′N, 45 m), Miyazaki (31°60′N, 40 m) and Naha (26°10′N, 5 m), and UV exposure was measured directly and estimated using outdoor‐activity records. The study site with largest UV exposure was Miyazaki, a southern rural area. Comparing the results for boys and girls, UV exposure was larger in boys. UV exposure was large in spring and summer and small in winter. The total amount of UV exposure in spring and summer contributed 57.7–73.4% of total exposure for the year. As a whole, 8.1% and 1.8% of the schoolchildren were exposed to more than 1 minimum erythemal dose (MED) and 2 MED of solar UV in a day, respectively. The estimated yearly UV exposure ranged from 49 207 J/m² in Miyazaki to 31 520 J/m² in Tsukuba. The actual UV exposure correlated to potential UV exposure, estimated using outdoor‐activity records and ambient UV irradiance, but the ratio differed by season and site. The yearly average of percent UV exposure to ambient UV on a horizontal plane ranged from 9.9% in Tokyo to 4.0% in Naha. In the questionnaire survey on outdoor‐activity pattern, a short question “How long did you spend time outdoors between 0900 and 1500 h?” gives the best estimates of UV exposure.     

Spectral UV irradiance on vertical surfaces: a case study

The UV spectral irradiance on horizontal and vertically oriented surfaces was measured throughout a cloudless day (18 July 1995) at Izana station, Tenerife, using a Bentham DTM300 spectroradiometer scanning from 290 to 500 nm in steps of 5 nm. Results show that irradiance measured on a horizontal surface is not proportional to irradiance on a vertical surface. The relation between the two depends upon orientation of the vertical surface, zenith angle and wavelength. At short UVB wavelengths surfaces directed toward the solar azimuth received their maximum irradiances much closer to solar noon than the maxima for longer wavelengths. Some vertical surfaces also received significantly more irradiance than the horizontal surface at long wavelengths during all but the central hours of the day, while at short wavelengths all vertical irradiances were less than the horizontal except for the measurements at the extreme ends of the day. Erythemally effective radiation followed the diurnal pattern of irradiations for short UVB wavelengths.     

Risk of Ocular Exposure to Biologically Effective UV Radiation in Different Geographical Directions

To quantify ocular exposure to solar ultraviolet radiation (UVR) and to assess the risk of eye damage in different geographical directions due to UVR exposure, we used a spectrometer and a manikin to measure horizontal ambient and ocular exposure UVR in different geographical directions at four different locations at the Northern Hemisphere. Describing the relationship of exposure to risk of eye damage requires the availability of UV hazard weighting function. So, we used the UV hazard weighting function (ICNIRP) proposed by International Commission on Non‐Ionizing Radiation Protection to determine the biologically effective UV irradiance (UVBE_eye) and then cumulative effective radiant exposure (H_eye) to shown the risk of eye. We found that in different geographical directions, distributions of ocular exposure to UVR were markedly different from those of horizontal ambient UVR. When the midday maximum SEA > 50°, eye received more UVR from the east and west directions during the morning and evening hours, respectively. However, when the midday maximum SEA < 50°, eye received more UVR from the south direction at noon. The results of this research indicate that the higher risk of eye caused by UVR varies according to the midday maximum SEA corresponding to different geographical direction.     

Diurnal variation of ocular exposure to solar ultraviolet radiation based on data from a manikin head

Measurements were conducted at San Ya, China (18.4°N, 109.7°E, altitude 18 m) to investigate the diurnal variation of ocular exposure to ultraviolet (UV) radiation. The experimental apparatus was composed of a manikin and a dual-detector spectrometer to simultaneously measure ocular and ambient UV data. The experimental apparatus was rotated clockwise to simulate three different types of exposure. When the manikin was facing into the sun, the ocular exposure to UV radiation on a summer day was bimodally distributed. The maximum ocular UV irradiance occurred at solar elevations of around 40° and 50° for UVA and UVB respectively. The spectral irradiances were measured at specific wavelength to obtain the ocular biologically effective UV (UV(BE) ) irradiances for photokeratitis, photoconjunctivitis and cataract, and the UV index (UVI) was calculated at the same time point for comparison. When the manikin faced the sun, the maximal ocular UV(BE) irradiance values were obtained at the solar elevation where the UVI value was 8. The results of this study showed that protection against ocular overexposure during outdoor activities should be taken not only at noon but also at other times.     

Sufficient Vitamin D from Casual Sun Exposure?

Next to the adverse effects of solar UV exposure, the beneficial effects mediated by vitamin D₃ have come into the limelight. The question then is “how much sun exposure do we actually need?” Estimates have been made, but the data are not quite adequate. The groups of Drs. Rhodes and Webb bridged the gap between experiments and everyday life by a study in which 109 volunteers were exposed in mid‐winter to simulated solar UV radiation in summertime clothing at dosages of 1.3 SED three times a week. Thus, 90% reached sufficiently high vitamin D statuses (>50 nmol L⁻¹). In this issue, these researchers transpose these experimental exposures in a cabinet to summertime noon exposures of people walking around for about half an hour in open terrain on a clear day in Manchester, UK. This result is an improvement over earlier estimates and shows that casual mid‐day summer sun exposure should indeed suffice.     

Modeling the anatomical distribution of sunlights

One of the major technical challenges in calculating solar irradiance on the human form has been the complexity of the surface geometry (i.e. the surface-normal vis-a-vis the incident radiation). Over 80% of skin cancers occur on the face, head, neck and back of the hands. The quantification, as well as the mapping of the anatomical distribution of solar radiation on the human form, is essential if we are to study the etiology of skin cancers or cataracts or immune system suppression. Using advances in computer graphics, including high-resolution three-dimensional mathematical representations of the human form, the calculation of irradiance has been attained to subcentimeter precision. Lighting detail included partitioning of direct beam and diffuse skylight, shadowing effects and gradations of model surface illumination depending on model surface geometry and incident light angle. With the incorporation of ray-tracing and irradiance algorithms, the results are not only realistic renderings but also accurate representations of the distribution of light on the subject model. The calculation of light illumination at various receptor points across the anatomy provides information about differential radiant exposure as a function of subject posture, orientation relative to the sun and sun elevation. The integration of a geodesic sun-tracking model into the lighting module enabled simulation of specific sun exposure scenarios, with instantaneous irradiance, as well as the cumulative radiant exposure, calculated for a given latitude, date, time of day and duration. Illustration of instantaneous irradiance or cumulative radiant exposure is achieved using a false-color rendering--mapping light intensity to color--creating irradiance or exposure isopleths. This approach may find application in the determination of the reduction in exposure that one achieves by wearing a hat, shirt or sunglasses. More fundamentally, such an analysis tool could provide improved estimates of scenario-specific dose (i.e. absorbed radiant exposure) needed to develop dose-response functions for sunlight-induced disease.     

Estimation of pedestrian level UV exposure under trees

Trees influence the amount of solar UV radiation that reaches pedestrians. A three-dimensional model was developed to predict the ultraviolet-B (UV-B) irradiance fields in open-tree canopies where the spacing between trees is equal to or greater than the width of individual tree crowns. The model predicted the relative irradiance (fraction of above-canopy irradiance) under both sunlit and shaded conditions under clear skies with a mean bias error of less than 0.01 and a root mean square error of 0.07. Both model and measurements showed that the locations people typically perceive as shady, low-irradiance locations in the environment can actually have significant UV-B exposure (40-60% of that under direct sunlight). The relationship of tree cover in residential neighborhoods to erythemal UV-B exposure for children and adults was modeled for the 4 h around noon in June and July. Results showed that human exposures (on the horizontal) in cities located at 15 and 30 degrees latitudes are nearly identical. For latitudes between 15 and 60 degrees, ultraviolet protection factors (UPF) were less than 2 for less than 50% tree cover. A UPF of 10 was possible at all latitudes for tree cover of 90%.     

Measurement of UVA Exposure to Solar Radiation

Exposure to solar UVA (320–400 nm) radiation can damage DNA and lead to skin disorders. Conventional dosim-etry using a single piece of polysulfone or diglycol carbonate (CR-39) cannot provide accurate measurement of the biologically effective irradiance for erythema for the UVA waveband. A package employing four dosimeters (polysulfone, nalidixic acid, 8-methoxypsoralen and phe-nothiazine) has been shown to be effective for use as a spectrum evaluator for evaluating the UVA source spectrum. In Brisbane, on a horizontal position, the spectrum evaluator requires about 5 min exposure in summer and about 20 min in winter. This amounts to about 10 mJ cm-² of erythemal UV radiation.     

Solar UV Exposure of Seafarers along Subtropical and Tropical Shipping Routes

Seafarers working on decks of vessels at low latitudes are exposed to extremely high solar UV radiation. Their risk of developing skin cancer may be enhanced. Solar erythemal UV irradiance and exposure were measured for the first time on merchant vessels going along typical international routes at low latitudes. The measurements taken at horizontal incidence on the observation deck, and on different parts of the seaman (head, shoulder, chest and back) doing typical outdoor work show the highest portion (40–80% of horizontal exposure) incident on the head. 2 years of measurements of solar UV and VIS/NIR irradiance taken on the mast top of the Research Vessel METEOR were added to the data base. Radiative transfer model calculations were performed along all the routes with satellite‐based input data of ozone and aerosol for clear sky health‐effective radiation including vitamin D3 (VD3). Measured data show extremely high noontime UV index values up to 19 with clear sky, and up to 22 due to cloud scattering. Eight hours erythemal exposure values are more than double of typical midlatitude summer values. Based on the results, an algorithm is presented to derive a seafarer's personal erythemal exposure according to his/her personal record of sea service.     

Comparison of GOME-2 UVA Satellite Data to Ground-Based UVA Measurements in South Africa

Satellite estimates of surface ultraviolet A (UVA) (315–400 nm) from the Global Ozone Monitoring Experiment (GOME)-2 were compared to ground-based measurements at four stations in South Africa for 2015. The comparison of daily exposure and daily maximum irradiance was completed for all-sky and clear-sky conditions. There is a strong linear correlation between the satellite and ground-based data with a correlation coefficient (r) between 0.86 and 0.97 for all-sky conditions. However, at three of the stations the satellite data are underestimated compared to ground-based data with a mean bias error (MBE) between −8.7% and −20.6%. A seasonal analysis indicated that there is a link between the bias in ground-based and GOME-2 UVA and cloud fraction. Factors such as aerosols, surface albedo, altitude and data resolution may contribute to the underestimations found at the three sites. These results indicate that satellite estimates of surface UVA over South Africa do not exhibit the same behavior as other stations around the world and therefore require further validation.     

Estimating the Diurnal Cycle and Daily Insolation of Ultraviolet and Photosynthetically Active Radiation at the Sea Surface

Accurate determination of the diurnal variability and daily insolation of surface (0⁺) and subsurface (0^?) irradiance are essential to estimate several physical, chemical and biological processes occurring at the surface layer of marine environments. Natural downwelling PAR and spectral UVR were examined on eight occasions at 0⁺ and 0^? to refine empirical models, particularly in the UVR spectrum. The diurnal variability in UVR and PAR were wavelength dependent and were modeled by a sinusoidal equation. The best fit for PAR at 0⁺ and 0^? was the sinusoid power of n = 2 and n = 2.5, respectively. In the UVR spectrum, sinusoids increased as wavelengths decreased ranging from n = 2–5. Higher n values in the UV‐B spectrum suggest sharper increase/decrease near sunrise and sunset hours, ultimately reducing the final value of daily insolation at specified wavelengths. Calculated daily insolation of UV‐B/(UV‐A + PAR) ratio suggests that photoinhibition from exposure to UV‐B occurs within a shorter biologically effective day length than PAR, and is high during summer and low during winter. These results suggest that biogeochemical calculations based on diurnal models of irradiance measurements would benefit from accurate solar noon references and wavelength specificity, particularly in the UVR spectrum.     

The Value of the Ratio of UVA to UVB in Sunlight

The objective of this communication is to present the calculated ratio between UVA and UVB irradiance from sunrise to sunset and under a number of weather conditions. UVA plays an important role in the sun spectrum and a lot of attention has been paid lately regarding the protection of people from UVA. Solar spectra were collected in Kuwait City located at 29.3^oNorth latitude (similar to that of Houston, TX) over a period of 8 months and under various weather conditions. Spectra were collected from 260 nm to 400 nm in 2 nm increments for solar elevation angles from 10^o to 90^o using a calibrated Optronics Laboratories OL‐742 Spectroradiometer. The measurements reported in this study the ratio of UVA (320–400 nm) to UVB (280–320 nm) in solar terrestrial radiation remains essentially constant and equal to 20 for the part of the day when the solar elevation is greater than 60^o. Consequently the value of the ratio of solar UVA/UVB should be considered as equal to 20 for studies in photobiology and photomedicine. When the wavelength limiting the range of UVA and UVB is 315 nm (i.e. UVB: 280–315 nm and UVA: 315–400 nm) the ratio of UVA to UVB becomes equal to 41.     

Seasonal Minimum and Maximum Solar Ultraviolet Exposure Measurements of Classroom Teachers Residing in Tropical North Queensland,Australia

The risk of keratinocyte skin cancer, malignant melanoma and ultraviolet radiation (UVR)‐induced eye disease is disproportionately higher in Australia and New Zealand compared to equivalent northern hemisphere latitudes. While many teachers are aware of the importance of reinforcing sun safety messages to students, many may not be aware of the considerable personal exposure risk while performing outdoor duties in locations experiencing high to extreme ambient UVR year‐round. Personal erythemally effective exposure of classroom teachers in tropical Townsville (19.3°S) was measured to establish seasonal extremes in exposure behavior. Mean daily personal exposure was higher in winter (91.2 J m^‐2, 0.91 Standard Erythema Dose [SED]) than summer (63.3 J m^?2, 0.63 SED). The range of exposures represents personal exposures that approximate current national guidelines for Australian workers at the study latitude of approximately 1.2 SED (30 J m^?2 effective to the International Commission on Non‐Ionizing Radiation Protection). Similar proportions of teachers spent more than 1 h outdoors per day in winter (28.6%) and summer (23.6%) as part of their teaching duties with seasonal differences having little effect on the time of exposure. Personal exposures for teachers peaked during both seasons near school meal break times at 11:00 am and 1:00 pm, respectively.