L. J. B. McArthur

McMaster University, Hamilton, Ontario, Canada

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Publications (14)18.57 Total impact

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    ABSTRACT: The sunphotometer Earth atmosphere measurement (SPEAM-I) experiment was flown on the United States space shuttle Challenger in October, 1984 as part of a group of Canadian experiments referred to as CANEX-I. Measurements of the solar intensity were made through the orbiter side-hatch window at various wavelengths in the visible and near-ultraviolet during a number of terminator crossings using a hand-held, interference filter photometer. Observations at 315 and 324 nm were analyzed to give vertical profiles of ozone at 63.34°S, 91.96°E. These profiles are compared with data from the literature. The success of this experiment points the way to the use of small instruments to make accurate but inexpensive observations of the composition of the upper atmosphere.
    Canadian Journal of Physics 02/2011; 69:1123-1127. · 0.90 Impact Factor
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    V E Fioletov, L J B McArthur, T W Mathews, L Marrett
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    ABSTRACT: Solar UV radiation is a major provider of vitamin D for humans. This study examines the distribution of solar UV radiation weighted according to the vitamin D action spectrum over the USA and Canada. Hourly and daily doses of spectrally integrated UV irradiance using the vitamin D action spectrum were estimated using a statistical relationship between UV irradiance and global solar irradiance, total ozone, and dew point temperature for 45 sites in Canada and 52 in the USA. Brewer spectrophotometer measurements at 12 sites in Canada and 21 sites in the USA were used to validate the obtained results. Different characteristics of the vitamin D action spectrum-weighted UV irradiance distribution over North America are presented in the form of monthly maps and as a data file. The time required to obtain standard vitamin D dose is also calculated for six types of skin.
    Journal of photochemistry and photobiology. B, Biology 08/2010; 100(2):57-66. · 3.11 Impact Factor
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    J. A. DAVIES, R. SCHROEDER, L. J. B. McARTHUR
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    ABSTRACT: Spectral optical depth measurements at Hamilton, Ontario in 1981 and 1983 are used to estimate stratospheric aerosol optical depths and a particle size distribution for the period of maximum stratospheric perturbation by aerosol due to the El Chichon eruption. Results are generally in good agreement with high altitude measurements and estimates. On average, stratospheric optical depth increased by about 0.08 with little spectral variation. Maximum aerosol enhancement occurred between January and May 1983. Mean optical depths for this period were inverted by the constrained linear inversion method of King. The resulting size distribution was similar to the haze H form of the incomplete distribution. It compared favourably with a distribution obtained by inverting NASA CV990 optical depth measurements and was similar to estimates based on direct aerosol measurements by aircraft and balloon.
    Tellus B 01/2010; 40B(2):154 - 160. · 3.20 Impact Factor
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    V E Fioletov, L J B McArthur, T W Mathews, L Marrett
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    ABSTRACT: Erythemally weighted solar ultraviolet (UV) radiation is often used to characterize the production of vitamin D in a human body. However, the vitamin D production action spectrum is different than that for erythemal UV. The vitamin D action spectrum weighted UV is more sensitive to UV-B, while the erythemal UV action spectrum has higher weighting coefficients than the vitamin D action spectrum in the UV-A part of the spectrum. Therefore, by using the erythemal UV as an estimate for the vitamin D action spectrum weighted UV can give results that differ by up to a factor of 5. This study examines the relationship between erythemal and vitamin D action spectrum weighted UV radiation using measurements of spectral UV at the surface by Brewer spectrophotometers that are part of the US and Canadian observational networks. It is shown that the ratio of vitamin D action spectrum weighted UV to erythemal UV is nearly constant for high levels of UV (UV Index greater than 5.5) and therefore vitamin D action spectrum weighted UV can be described in terms of erythemal UV. For lower levels of UV though this relationship should not be used. A simple formula that calculates vitamin D action spectrum weighted UV from UV Index is developed. An empirical formula that expresses the ratio of vitamin D action spectrum weighted UV to erythemal UV as a function of the solar zenith angle and column ozone is also suggested. The geographical distributions of vitamin D action spectrum weighted UV in the US and Canada are discussed.
    Journal of photochemistry and photobiology. B, Biology 01/2009; 95(1):9-16. · 3.11 Impact Factor
  • L J B McArthur, D I Wardle, C T McElroy, J B Kerr
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    ABSTRACT: The use of self-scanning photodiode arrays is well established for low light intensity multi-spectral measurement systems such as those used in spectroscopy and astronomy. Using the newly developed EG&G Reticon random access self-scanning linear photodiode array, an instrument has been developed for solar observations which overcomes the difficulties associated with these detectors at high light levels. By coupling this technology with flat-field concave holographic grating technology from American Holographic, a "sunphotospectrometer" has been built. This instrument is presently able to scan 1 024 channels of spectral information in less than 1 s. A prototype instrument is being tested with a second-generation version expected to fly aboard the US Space Shuttle within the next two years. The design of this instrument is described and preliminary spectra are presented to illustrate the measurement of NO2 using this portable system.
    Metrologia 01/2005; 28(3):291. · 1.90 Impact Factor
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    ABSTRACT: [1] Long-term monthly mean UV index values for Canada and the United States were calculated using information from two sources: from noon erythemal UV estimated from Total Ozone Mapping Spectrometer (TOMS) total ozone and reflectivity data and from UV index values derived from observations of global solar radiation, total ozone, dew point, and snow cover. The results are presented as monthly maps of mean noon UV index values. Mean UV index values in summer range from 1.5 in the Arctic to 11.5 over southern Texas. Both climatologies were validated against spectral UV irradiance measurements made by Brewer spectrophotometers. With snow on the ground the TOMS-based data underestimate UV by up to 60% with respect to Brewer measurements and UV derived from global solar radiation and other parameters. In summer, TOMS UV index climatology values are from 10 to 30% higher than those derived from global solar radiation and other parameters. The difference is probably related to aerosol absorption and pollution effects in the lower troposphere that are not currently detected from space. For 21 of 28 midlatitude Brewer sites, long-term mean summer UV measured values and UV derived from global solar radiation and other parameters agree to within +5 to −7%. The remaining seven sites are located in “clean” environments where TOMS estimates agree with Brewer measurements while UV derived from global solar radiation and other parameters is 10–13% lower. Brewer data also demonstrate that clean and “typical” sites can be as little as 70–120 km apart.
    11/2004; 109(D22).
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    ABSTRACT: Hourly UV Index values at 45 sites in Canada and 52 in the USA were estimated using a statistical relationship between UV irradiance and global solar radiation, total ozone, and dew point temperature. The estimation method also takes into account the enhancement of UV irradiance by snow using an empirical correction derived from Brewer UV measurements. Different characteristics of the UV Index distribution over North America were estimated from the derived UV irradiance for the period 1979-1987 and then presented in the form of monthly maps. Brewer UV measurements at 11 Canadian and 20 US sites and erythemal UV estimates from TOMS data were used for validation. Direct comparisons with Brewer measurements at 7 Canadian sites for the period in the 1990s when both pyranometer and spectral UV data were available demonstrated agreement within 2-3 percent except for periods of melting snow when variations in snow albedo yield higher errors in the derived UV irradiance.
    Proc SPIE 11/2003;
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    ABSTRACT: An improved understanding of the global ultraviolet (UV) climate has recently become of great interest. A number of stations are now making regular measurements of spectrally‐resolved UV‐B irradiance. Despite the lack of long‐term records, it is possible to describe many of the short‐term characteristics, dependencies and climatology of surface UV‐B irradiance. This article describes the current state of UV‐B measurements, and a climatology of surface UV‐B irradiance with particular focus on Canada. The dependence of UV irradiance on ozone and other climate variables is discussed in detail, with reference to observations. In addition, comparison of radiative transfer models with recent measurements indicates that it is possible to infer surface UV‐B irradiance from older records of total ozone and ancillary measurements (spectrally‐integrated irradiance, aerosol optical depth and surface albedo) permitting the derivation of longer‐term trends.
    Atmosphere-Ocean. 01/2003; 41(2):121-138.
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    ABSTRACT: Hourly UV index values at 45 sites in Canada were estimated using a statistical relationship between UV irradiance and global solar radiation, total ozone, and dewpoint temperature. The estimation method also takes into account the enhancement of UV irradiance by snow using an empirical correction derived from Brewer UV measurements. Different characteristics of UV index distribution over Canada were estimated from the derived UV irradiance for the period 1979-87 and then presented in the form of monthly maps. Direct comparisons of Brewer measurements at seven Canadian sites with derived UV irradiance show agreement within 2%-3% except for periods of melting snow when variations in snow albedo yield higher errors in the derived UV irradiance.
    Journal of Applied Meteorology 01/2003; 42(3):417-433.
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    ABSTRACT: Routine standard spectral UVB measurements with Brewer spectrophotometers in the Canadian network began in 1989. The time interval of UV measurements militates against reliable detection of long-term changes in UV. To estimate the UV irradiance (at individual wavelengths and spectrally integrated) values prior to 1989 a statistical model has been developed to derive UVB from other variables, which have been measured since the 1960s. These variables include global solar radiation, total ozone, dew point temperature, and snow cover. The model results are demonstrated to be in good agreement with the measurements since 1989. For example, the standard deviations of the difference between monthly values of measured and derived erythemaly weighted UV irradiation is 3.3% for summer months. The major source of error in the model estimates is likely linked to rare occurrences of absorbing aerosols in the atmosphere. Long records of reliable measurements of total ozone, global solar radiation and other parameters made it possible to derive UVB values at three Canadian stations from the mid 1960s. Trends in derived erythemaly weighted UV at two stations (Toronto and Edmonton) are similar to those expected from total ozone trends although the estimated error of the UV trends is more than 2 times larger. However the increase in annual UV at Churchill (59 N) in 1979-1997 was found to be more than twice that expected from the ozone decline. This is a result of long-term changes in snow cover and clouds.
    Proc SPIE 01/2002;
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    V. E. Fioletov, L. J. B. McArthur, J. B. Kerr, D. I. Wardle
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    ABSTRACT: Routine uniform spectral UV-B measurements with Brewer spectrophotometers in the Canadian network began in 1989. This relatively short duration of UV measurements militates against reliable detection of long-term changes in UV. A statistical model has been developed to extend the record of UV back to the early 1960s. It estimates UV values (at individual wavelengths and spectrally integrated) from global solar radiation, total ozone, dew point temperature, and snow cover. The model results are demonstrated to be in good agreement with the measurements. For example, the standard deviation of the difference between monthly values of measured and derived erythemally weighted UV irradiation is 3.3% for summer months. The major source of error in the model estimates is probably linked to rare occurrences of absorbing aerosols in the atmosphere. Long records of reliable measurements of total ozone, global solar radiation, and other parameters made it possible to derive UV-B values at three Canadian stations from the mid-1960s. Trends in derived erythemally weighted UV at two stations (Toronto and Edmonton) are similar to those expected from total ozone trends although the estimated error of the UV trends is more than 2 times larger. However, the increase in annual UV at Chruchill (59°N) in 1979-1997 was found to be more than twice that expected from the ozone decline. This is a result of long-term changes in snow cover and clouds.
    Journal of Geophysical Research 01/2001; 106:23009-23028. · 3.17 Impact Factor
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    ABSTRACT: Two statistical models have been developed from 6 years of simultaneous measurements of global radiation by pyranometers, UV-A by a Brewer spectrophotometer and from total ozone, dew point temperature and snow cover data at Toronto. The models estimate instantaneous UV-A irradiance at 324 nm from pyranometer data with an uncertainty as low as 3.5% (1σ) for summer sunny conditions and between 6–10% for cloudy conditions. These uncertainties are reasonably small when compared with the uncertainty of UV-A and global solar irradiance measurements (2–3%). The uncertainty is reduced when daily and longer-term averages are considered. The major source of error in the models is likely linked to rare occurrences of absorbing aerosols in the atmosphere. The models were also tested on a 6-year, independent record from Edmonton. The uncertainties at Edmonton are 30–45% larger than at Toronto for the instantaneous data, approximately 20% larger for daily integrated values.
    Journal of Geophysical Research 01/1999; 104:30139-30151. · 3.17 Impact Factor
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    ABSTRACT: Following the success of the Sunphotometer Earth Atmosphere Measurement (SPEAM-I) experiment, a more involved experiment was developed to fly as part of the second set of Canadian Experiments (CANEX-2) which will fly on the US Space Shuttle in the fall of 1992. The instrument complement includes an IBM-PC compatible control computer, a hand-held diode array spectrophotometer, and an interference-filter, limb imaging radiometer for the measurement of the atmospheric airglow. The hand-held spectrometer will measure nitrogen dioxide, ozone and aerosols. The limb imaging radiometer will observe emissions from the O2(1 DELTA) and O2(1 SIGMA) airglow bands. Only the spectrophotometer will be discussed here.
    04/1994;
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    ABSTRACT: Long-term monthly mean UV index values for Canada and the United States were calculated using information from two sources: from noon erythemal UV estimated from Total Ozone Mapping Spectrometer (TOMS) total ozone and reflectivity data and from UV index values derived from observations of global solar radiation, total ozone, dew point, and snow cover. The results are presented as monthly maps of mean noon UV index values. Mean UV index values in summer range from 1.5 in the Arctic to 11.5 over southern Texas. Both climatologies were validated against spectral UV irradiance measurements made by Brewer spectrophotometers. With snow on the ground the TOMS-based data underestimate UV by up to 60% with respect to Brewer measurements and UV derived from global solar radiation and other parameters. In summer, TOMS UV index climatology values are from 10 to 30% higher than those derived from global solar radiation and other parameters. The difference is probably related to aerosol absorption and pollution effects in the lower troposphere that are not currently detected from space. For 21 of 28 midlatitude Brewer sites, long-term mean summer UV measured values and UV derived from global solar radiation and other parameters agree to within +5 to −7%. The remaining seven sites are located in "clean" environments where TOMS estimates agree with Brewer measurements while UV derived from global solar radiation and other parameters is 10–13% lower. Brewer data also demonstrate that clean and "typical" sites can be as little as 70–120 km apart.