Importance of UV Monitoring

        The purpose of ground-level monitoring of UV radiation in parks is twofold: (a) to determine spatial and temporal trends in UV reaching the ground at different elevations and in different environments, and (b) to provide an estimate of the exposure of park resources to UV-B to determine dose-response relationships. It is widely documented that stratospheric ozone has been reduced due to the release of chlorofluorocarbons into the atmosphere. It is also known that this reduction in total column ozone has resulted in increasing amounts of UV-B reaching the surface, with the largest changes being observed in the polar regions. There is evidence that these higher levels of UV-B radiation can be detrimental to human health and biological resources. Resources that have been identified as sensitive to increased UV-B include amphibians, arid-land reptiles, and marine and freshwater plant and animal populations.  In human populations, increases in UV-B are linked to higher incidence of skin cancer, cataracts, and immune system disorders.

        To increase our knowledge of the trends in this stressor and the possible consequences to natural resources, PRIMENet focuses both research and monitoring activities on this issue. In addition to the UV monitors placed in the national parks, the EPA has an existing, complementary network of UV monitors in urban areas. These include Boston, Massachusetts; Boulder, Colorado; Gaithersburg, Maryland; Research Triangle Park, North Carolina; Atlanta, Georgia; Riverside, California; and Albuquerque, New Mexico.  The urban monitors are used primarily to assess human exposure to UV-B radiation.  In addition to EPA, several other federal agencies are monitoring UV radiation, including the USDA, NOAA, the Department of Energy, the National Science Foundation and the Smithsonian. There are co-located UV instruments in both Big Bend and Everglades NPs, where the USDA is currently operating their "shadow band" instruments. A common web site for information on these UV networks can be found at http://www.arl.noaa.gov/research/ programs/uv.html. These agencies are coordinating activities through the "U.S. Interagency UV-Monitoring Network Plan" prepared under the auspices of the President’s Committee on Environment and Natural Resources.

 

        The contractor in charge of PRIMENet UV operations is the University of Georgia. The NPS coordinates the site operators and NOAA assists in the quality assurance and audit program. Overall project management is headed by the EPA-Global Change Program at the National Exposure Research Lab in Research Triangle Park, North Carolina.

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Monitoring System

        Each of the fourteen PRIMENet sites are equipped with a Brewer spectrophotometer, an instrument designed to measure different wavelengths of light, with a focus on the ultraviolet spectra (UV-B radiation is in the 300-320 nm range of light). These instruments actively track the sun as they monitor the variation in solar irradiance throughout the day; they also record other data, such as total column ozone and optical density. These data are then used to calculate the "dose" of UV at the surface of the earth. Because of the influence of sun angle, clouds and other forms of air pollution, the seasonal variation in UV-B detected at the surface is large. Therefore, it will take many years of monitoring to detect trends in the incidence of UV-B.                  

        During 1997, six Brewer spectrophotometers operated year-round in PRIMENet parks as part of the UV Network. Brewers have been installed in all of the remaining parks, the last of which was Hawaii Volcanoes NP in February 1999. 

 

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  UV Monitor Site Information. Data available at http://www.epa.gov/uvnet.

*Only Big Bend, Everglades, Great Smoky Mountains, and Shenandoah NPs were presented in Figures 7 and 8

        The following graphs show daily DUV integrals at four sites that had coverage over a significant portion of 1997. Each data point represents a 5-day running maximum of UV. The graphs display seasonal bell-shaped curves, with values highest in the summer and lowest in the winter. Big Bend NP had the highest reported DUV, even though Everglades is located farther south and Shenandoah NP had higher DUV than Great Smoky Mountains NP.

Daily DUV Integrals in 1997.

        The box and whisker plots shown in the following graphs summarize the spread of the data in months of the year. The box covers the middle 50% of the data (the middle two quartiles), with the median given by a hash mark and the mean by a "+". The whiskers extend to the most extreme data point or to 1.5 times the length of the box, whichever is less. Data points beyond the whisker are given individual symbols. The width of the box is proportional to the number of good data points. The envelope shape of the seasonal curve, monthly range of values, and peak DUV during the summer all varies for the four sites.

Statistical summary of the UV radiation in 1997; A. Big Bend NP; B. Great Smoky Mountains NP; C. Everglades NP; and D. Shenandoah NP.

Clouds and haze are major factors in determining the daily DUV and account for most of the variability during the month. Some facets of the climatology of the sites can be inferred from these plots.

        Although daily DUV is the total energy input, it is concentrated during mid-day when the sun is at minimum zenith angle, which is determined by the latitude of the site. Daily DUV is also determined by the length of the day. Therefore, a site like Denali NP will have a more pronounced seasonal cycle than a site like Everglades NP, but the summertime maximum values at Denali may be surprising high due to the length of day at that latitude. More information on the UV network is available at http://www.epa.gov/uvnet.

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UV Publications and Links of Interest

Natural Resource Information Division Fact Sheet, Measuring Ultraviolet Radiation in National Park Service Units

NOAA press release on Antartic ozone hole (* pdf file)

Information from Sci-Tec about the Brewer spectrophotometer. Or see the Sci-Tec home page.

US Global Change Research Program - The interagency ultraviolet radiation program is described in more detail at this web
site.

A centralized UV-B calibration facility is operated by NOAA for the calibration and intercomparison of the Brewer instruments and other UV-B instruments used by the interagency ultraviolet radion program. Their work and some pictures of their activities are presented.

* pdf files require the Adobe Acrobat reader to view and print. Get a free copy HERE.

 

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