Impact/Purpose:

The objective of this research task is to provide spectrally resolved UV-B and UV-A radiation data, on a daily basis from 21 disperse PRIMENet sites, that will be traceable to NIST standards and accepted as being of high and defensible quality by the international research community. The data collected from the 21 PRIMENet sites will be suitable for research into fundamental processes for understanding of UV flux in order to enable us to describe and model exposures of ecosystems and human beings to UV radiation.

The UV data collected from the 21 PRIMENet sites will help UV researchers in understaning and characterizing the factors, including optical transmission properties of aerosols, which affect the intensity of UV-B radiation measured at the earth's surface in order to improve our estimates of ecosystem and human exposures to UV-B radiation. The UV data will also help researchers to understand the relationship between UV radiation and total column ozone; to model UV-B exposures at different locations, conditions, and times in order to estimate UV-B exposures throughout the US. Additionally, the research program will enable the Agency to specify the actual levels of ultraviolet radiation as a stressor in the environment and to identify long-term trends in UV flux, if any, together with the associated causes for any such trends. A goal of this research program is to apply quality control and Level 1 correction factors to raw data in order to achieve archived data of the highest quality and reliability. The monitoring research described herein represents only a fraction of the UV related research conducted by EPA. Other efforts (for example, in NHEERL, in OAR, and with the National Park Service at the PRIMENet) are aimed at quantifying human and ecological effects of changes in UV radiation. The measurement effort is also being conducted in coordination with the Committee on Earth and Natural Resources (CENR), whose responsibility it is to coordinate the UV measurement efforts of all federal agencies. The major objective of this research task will be achieved by maintaining a strict quality assurance program for both the Brewer Spectrophotometers in the network and the UV data obtained by them.

Description:

Because exposure to ultraviolet (UV) radiation is an ecosystem stressor and poses a human health risk, the National Exposure Research Laboratory (NERL) has undertaken a research program to measure the intensity of UV-B radiation at various locations throughout the U.S. In September 1996, the National Park Service (NPS) and the Environmental Protection Agency (EPA) signed an interagency agreement (IAG) to cooperate on a program of long-term monitoring of environmental stressors at various sites throughout the U.S., and to undertake research on the effects of those stressors on ecosystems and human health. The EPA UV monitoring network is composed of 21 Brewer spectrophotometers deployed throughout the United States to measure full sky UV irradiances. Each site is comprised of a Brewer spectrophotometer mounted on a tracker and tripod unit which is controlled by a desktop computer running DOS and GW Basic Brewer software. The sites come under the joint EPA/NPS Park Research and Intensive Monitoring of Ecosystems Network (PRIMENet) [formerly Demonstration Intensive Site Project (DISPro)] network. Fourteen of the Brewer sites are located in U.S. National Parks, and seven of the Brewer sites are located in urban settings. Data from those 21 sites are being run through a quality assurance program to properly characterize UV radiation intensities at the earth's surface. This task covers: operation of the UV measurement site at RTP, NC; technical collaboration / interaction and data exchange with other researchers in the UV measurement field (including application of UV radiation standards and devices and intercomparison protocols); analysis of the UV-B data collected at the 21 PRIMENet sites; and research to understand and characterize the critical factors that affect the nature and intensity of the UV-B radiation measured at the earth's surface. The UV data being collected through this program is being used by NERL scientists to determine: the effect of UV radiation on microbial activity/growth and how that affects the availability of organic carbon is changed in coastal estuaries; the effect of spatial and temporal variation in UV exposure on coral reefs. The UV data being collected through this program is being used by NRMRL and NERL scientists to determine how UV-exposed, Chromated Copper Arsenate (CCA)-treated [pressure treated] wood surfaces can (through chemical reactions of the CCA) lead to dermal arsenic exposure for various subpopulations. North Carolina State University scientists are using the collected UV data to determine the effect that PM10 and black carbon has on the reduction of UV surface radiation. Due to fact that many different researchers and scientific organizations use the UV radiation data collected over time by this research, this research has been a long-term, ongoing program (1996 - 2005), which should continue into the forseeable future. By applying improved UV instrument measurement technology to this research program, it can continue to provide more complete, accurate and timely UV data to researchers.

NERL has undertaken this UV radiation research program in two separate, but related research tasks: Task 9423 (this research task) - a quality-assurance/quality control program responsible for: maintenance of the Brewer Spectrophotometer instruments; collecting the UV data from each of the 21 PRIMENet sites on a daily basis; providing Level 1 data correction to the raw UV data collected from the Brewer Spectrophotometers; development of wavelength intensity standards traceable to NIST standards (for the horizontal position to correlate with the Brewer's input optics); characterization of the Brewers for slit width, wavelength dependency for stray light, cosine response function for the input optics. Task 3900 - a process-oriented research program designed: a) to improve our understanding and description of the nature and intensity of UV-B radiation reaching the earth's surface; b) to characterize the physical and chemical parameters that modify and control the UV radiation flux; and c) to use our enhanced understanding of UV radiation in improving radiative transfer models to obtain better estimates of UV exposures at different times, locations and meterological conditions.

Record Details:

Record Type:PROJECT

Start Date:10/01/1998

Completion Date:09/01/2003

Record ID: 56204

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Project Information:

Progress :NERL has been involved in UV related research for a number of years. In response to directions from the Administrator of EPA, NERL developed plans in the late spring of 1992 to establish a UV Exposure Index and Monitoring Network. The focus of the program was to assist the Office of Air and Radiation in informing the public of the potential for UV exposure and to provide a firm scientific and measurement basis for describing the impacts of changes in stratospheric ozone on UV exposures and effects. The information part of the program was a cooperative effort involving Office of Research and Development (ORD), Office of Air and Radiation (OAR), and the National Weather Service (NWS) to develop an exposure "Index." Through an Interagency Agreement, NERL previously requested NWS to develop the predictive Index and funded NWS in their UV modeling and in their development of products to be disseminated as part of the daily weather forecast. NERL helped refine and validate the NWS Index model by providing data from the our ground-monitoring site in Research Triangle Park (RTP), North Carolina. The monitoring network was designed to provide the scientific basis for the UV exposure "Index"; to verify the predictions of potential human UV exposure; to assess and improve the algorithms for predicting the UV flux, accounting for pollutants and other factors in populated areas; and to provide high-quality, spectrally-resolved UV radiation measurements that can be convolved with a variety of human health or biological action curves, either known now, or to be developed in the future.

A preliminary EPA network design called for research-grade, spectrally resolved UV monitors in urban areas and in rural or clean, background sites. The urban sites were chosen to represent more than 25% of the US population. The EPA UV measurement network was coordinated with other U.S. measurement efforts under the Committee on Environment and Natural Resources (CENR). An interagency UV-monitoring plan was developed to coordinate UV monitoring within the U.S. As part of the CENR coordination, EPA/ORD and other federal agencies making UV measurements signed a memorandum of understanding (MOU) with the National Oceanic and Atmospheric Administration (NOAA) to financially support the development and operation of a Central Ultraviolet Calibration Facility (CUCF) at the NOAA laboratory in Boulder, CO. This facility allows intercomparability of our UV data with that of other agencies and provides the EPA program with external audits of the Brewers at the field sites.

Long-term monitoring of UV radiation is necessary to detect trends that may be produced as a result of changes in stratospheric ozone. The effect of stratospheric ozone is to drastically reduce the amount of UV radiation of shorter wave lengths (i.e., UV-B) from reaching the earth's surface. It is precisely the shorter wave length radiation that can be the most biologically damaging. High-quality, spectrally-resolved data are necessary to assess how changes in total column ozone or other factors are likely to interact with the action spectra of biological or other systems to produce an effect. A detailed quality control (QC) and data correction program is conducted at the University of Georgia at Athens (UGA) on the UV data collected from the network. All corrected data are transferred to EPA, and the corrected data from the network is posted to an EPA web site that is accessible to the general public. To access the (Level 1 corrected) UV data collected at all of the PRIMENet sites on the Internet, you must go to the following web page: http://www.epa.gov/uvnet/access.html . The UV data for each site is also provided to EPA on CD-ROMs by the contractor (UGA). The structure of the UV data displayed on the public web page (and files, formats, etc.) and the content is exactly the same as on the CD-ROMs.



Relevance : This research effort relates principally to EPA's Government Performance and Results Act (GPRA) Goal Number 6, "Reducing Global and Transboundary Environmental Risks." Under this goal, the work supports Objective #3, "By 2000 and beyond, US greenhouse gas emissions will be reduced to levels consistent with international commitments agreed upon under the Framework Convention on Climate Change, building upon public health and ecosystem assessment efforts under the Climate Change Action Plan." ORD's sub-objective # 3.3 states "By 2000 and beyond, ORD will provide the capability to assess ecological and associated human health vulnerability to climate-induced stressors at the regional scale and assess mitigation and adaptation strategies." Stratospheric ozone, addressed under the Climate Change Action Plan, is the principal barrier to excessive UV radiation reaching the earth's surface, since ozone strongly absorbs UV radiation in the atmosphere. As stratospheric ozone is depleted and / or restored, UV radiation and UV exposures are anticipated to change accordingly. This research will characterize the UV radiation actually reaching the earth's surface and relate it to any changes in total column ozone or other factors which can mitigate or exacerbate the resultant exposure. The data to be produced under this effort will significantly affect the Agency's ability to assess ecological and associated human health vulnerability due to changes in stratospheric ozone.

Decreases in the quantity of total-column ozone, as now observed in many places, tend to cause increased penetration of solar UV-B radiation (280-315 nm) to the Earth's surface. UV-B radiation is the most energetic component of sunlight reaching the surface. It has profound effects on human health, animals, plants, microorganisms, materials and on air quality. Thus any perturbation which leads to an increase in UV-B radiation demands careful consideration of the possible consequences.

For global UV radiation reaching the earth's surface, verification of long-term UV trends by direct measurement is required. UV radiation affects human health and ecological issues such as infectious diseases, vaccination efficacy, cataract and melanoma incidence, aquatic and terrestrial ecosystems, food production and biodiversity. It is clear that these research areas require long-term studies of UV trends for meaningful results to be obtained.

Clients : NERL (Sharon Harper), NRMRL (Mark Mason), NCSU (Bill Barnard), OAR (Terry Keating), ERD (Richard Zepp)

Project IDs:

ID Code :9423

Project type :OMIS