Environ. Sei. Technol. 1983, 17, 127-128
(4) Fishman, M. J.; Erdmann, D. E.; Steinheimer, T. R. Anal. Chem. 1981,53, 198R-200R. ( 5 ) Beggs, D. P. Am. Lab. 1978,81-87. (6) Westendorf, R. G. “Optimization of Parameters for Purge and Trap Gas Chromatography”, Tekmar Corp., Cincinnati, OH, 1981. (7) “Handbook for Analytical Quality Control in Water and Wastewater Laboratories”,US.Environmental Protection Agency, Environmental Monitoring Support Laboratory, Cincinnati, OH, EPA-600/4-79-019, 1979; pp 6-12.
mended that the U S . EPA Quality Assurance flowchart involving laboratory and field spikes and blanks (7) be strictly followed for all method 601 and 602 samples. Registry No. Dichloromethane, 75-09-2;trans-1,2-dichloroethylene, 156-60-5; chloroform, 67-66-3; 1,2-dichloroethane, 107-06-2;Teflon, 9002-84-0. Literature Cited (1) Fed. Regist. 1979, 44, Appendix I, 69468-69473. (2) Fed. Regist. 1979, 44, Appendix I, 69474-69478. (3) Bellar, T. A,; Lichtenberg, J. J. J. Am. Water Works Assoc. 197466, 739-744.
Received for review June 1 , 1982. Accepted November 5, 1982. Materials Co., Findlay, OH. This research supported by O.H.
A Simple and Inexpensive Method for Measuring Integrated Light Energy Timothy J. Sullivan” and Mlchael C. Mix
Department of General Science, Oregon State University, Corvallis, Oregon 97331
w The ozalid technique is a simple and inexpensive me-
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thod for measuring integrated sunlight energy in the field for periods up to a maximum of 1 day. This paper describes a modification of the ozalid technique that makes it suitable for long-term light measurements. Data from the modified ozalid meter were calibrated against an Eppley Precision Spectro Pyranometer, yielding a strong positive correlation (R2= 0.97).
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Introduction
The measurement of light energy from the sun is an important consideration in a variety of environmental field investigations, ranging from ecological studies of primary productivity to photodegradation of chemicals in the environment. Unfortunately, the equipment needed to measure integrated light energy is expensive and not easily transported into the field. Also, it is often advantageous to obtain numerous light readings simultaneously from different study areas, which may be cost-prohibitive. This paper describes a simple and inexpensive method for measuring integrated sunlight energy in the field for periods ranging up to 40 days. Friend (1)proposed the use of photosensitive ozalid paper for measuring light for short periods of time to a maximum of approximately 1 day. We employed stacks of aluminum screening as a neutral density filter, thereby substantially reducing the amount of solar radiation. With this adaptation the ozalid meter can be used accurately for long-term light measurements. Experimental Section
The adapted ozalid meter consists of a stack of 12 sheets of ozalid paper (Shannon and Co., Portland, OR) stapled into a booklet approximately 2 cm X 3 cm with the yellow side up. The ozalid stack is then sandwiched between two discs of black paper, with two small holes (approximately 0.5 cm) punched through the top disc directly above the ozalid stack. A stack of 10 aluminum screens (mesh size 7/cm) with alternating cross-hatching is placed above the top disc, and the entire apparatus is placed in a glass petri dish. Foam rubber or plastic in the bottom of the petri dish will hold the stacks in position. The petri dish is then secured with electrical tape to keep the ozalid paper dry 00 13-936X/83/09 17-0127$01.50/0
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Flgure 1. Incoming solar energy due to total visible light (0.295-2.9 pm) (A) and due to the 0.295-0.530-pm portion of the electromagnetic spectrum (B), expressed as a function of number of ozalid sheets developed. R 2 values equal 0.973 and 0.971, respectively.
in the event of precipitation. The cost for each meter is only a few cents for materials other than the petri dish. Upon exposure to light the ozalid sheets are bleached from yellow to white beneath the holes in the black disc. When the exposure period is completed, the stacks are removed in dim light, labeled and developed in ammonia vapor for 10-20 min (see Friend (1)for instructions on assembling a simple developing jar). The number of positive ozalid sheets (those identified as exposed after development) can then be counted and the degree of development of the last sheet estimated to the nearest 1/4 sheet. It is advantageous to first select standards to represent lI4, l J 2 , and 3 / 4 development, and mount these standards so they may be viewed for easy comparison with test papers. Since there may be slight differences in results between “ozalid meters”, each light measurement should be taken with 3-5 replicates. A mean value for number of positive ozalid sheets is then converted to incoming solar
0 1983 American Chemical Society
Environ. Sci. Technol., Vol. 17, No. 2, 1983
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energy by using a calibration curve.
Results and Discussion Data from the preceding method were calibrated against an Eppley Precision Spectro Pyranometer operated by the Department of Atmospheric Science, Oregon State University. When plotted on a log scale, solar energy (kJ/m2) is a linear function of the number of ozalid sheets developed for both total visible (0.295-2.8 pm) and for the more biologically active (0.295-0.530 pm) portion of the electromagnetic spectrum (Figure 1). The following relationships were obtained ( n = 14):
+ 5.125 In E0.2954.530 = 0.965X + 3.793 In Etotal = 0.963X
R2 = 0.973 R2 = 0.971
(1) (2)
where X = mean number of ozalid sheets developed for two light meters. Meters employing stacks of six and eight aluminum screens were also calibrated, yielding similar linear relationships (R2= 0.95-0.96). Although no attempt was made to standardize screen placement, other than alternating cross-hatching, light meter results seldom varied by more than one-quarter of a sheet (i.e., 4%). This
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indicates that screen placement is not a critical factor for light meter precision. The above calibration relationships indicate the reliability of this method for estimating solar energy in the field from total visible and 0.295-0.530-pm electromagnetic radiation. Its simplicity and low cost make this a practical tool for a variety of environmental field studies.
Acknowledgments
C. R. N. Rao generously provided data from the spectro pyranometer (sponsored by the Solar Energy Meteorological Research and Training Site, Division of Distributed Solar Technology, U.S. Department of Energy). Helpful suggestions were provided by D. Brooker and D. Zobel. Literature Cited (1) Friend, D.C . Ecology 1961, 42, 577-580. Received for review June I , 1982. Accepted November 8, 1982. This research was sponsored in part by a cooperative Agreement, CR808000-01-0, in the NCIIEPA Collaborative Program Project No. 3 (“Effects of Carcinogens, Mutagens, and Teratogens in Non-human Species and Aquatic Animals”), administered by the Gulf Breeze, FL, Environmental Research Laboratory.
