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UV RADIATION MEASUREMENTS/ATMOSPHERIC CHARACTERIZATION
To understand and characterize 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; 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. This objective is achieved by maintaining a strict quality assurance program for both the Brewer Spectrophotometers in the network and the UV data obtained from the Brewers.
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 the Disk Operating System (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.
NERL has undertaken this UV radiation research program in two separate, but related research tasks: Task 3900 (this research task) - 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; Task 9423 - 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.
This task covers: operation of the UV measurement site at Research Triangle Park (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.