A Simple UV Experiment of Environmental Significance D., W. Daniel GMI Engineering and Management Institute, Flinf, MI 48504 ~ l i s h aG. Allen, Gregory R'; Brown; Hareesh Chandrupatla, Steve A. Fowler, Deondre J. Richmond, Shaun W. Skipper, Jason A. Taylor, and Amy E. Wasiak, Participants GMI Engineering and Management Institute, 1992 Young Scholars Program, Flint, MI 48504 Stratospheric ozone blocks harmful ultraviolet radiation that has been linked to health problems in living organisms and the deterioration of manmade materials ( I ) . Because of the beneficial screening ability of ozone, its depletion h a s been t h e focus of worldwide concern a n d legislation (2). As part of GMI's NSF-funded Young Scholars program focusing on environmental issues, our research group developed a technique to illustrate how sunscreens and ozone qualitatively compare in UV-blocking ability. Ozone Production and Analysis A piece of copper wire is placed in an ambient air-filled gas cell to aid in the direction of the high voltage discharge. Figure l a illustrates the positioning of a Tesla coil in a permanently sealed cell. The Tesla coil is held in this position on its highest setting. The distinct odor of ozone and a blue glow within the cell during charging confirms the pmdnction of the gas (3).ARer 60 s the coil is removed and the stopcock is quickly inserted and closed to contain the gas. An alternative method of capturing ozone in cells with removable windows is shown in Figure lb. One window is removed and the Tesla coil is discharged deep within the analysis area. This method requires no metal wire since the discharge and ozone production occur within the sample area of the cell. Rapid resealing msures a n adequate concentration of ozone. Figure 2a shows the background corrected UV spectrum of the 0 3 containing cell. UV absorption in the 220-300 nm range is observed.
Ulavelenqth
(nm)
Figure 2. (a)Ozone spectrum. (b)Spectrum of a typical sunscreen. Analysis of Sunscreens Sunscreens of varying sun protection factors (SPFs) and several tanning oils were examined by UV for both comparison between them and with the ozone. The sunscreens were thinly coated onto clean UV windows and examined in the instrument. The spectrum of a representative sunscreen is shown in Figure 2b. As with the ozone, the spectrum was baseline corrected by reference to the clean window. Conclusions All of the sunscreens tested (SPFs 1 5 4 5 ) showed essentially the same energy absorptions. It is interesting to note that although both the sunscreens and ozone absorb energy in the UV region, their energy absorption ranges are complementary. Ozone absorption in the 220-300 nm range correlates to the minimum absorption for the sunscreens. Although the data are not shown here, the tannine .. oils that were tested did not absorb in the UV. This experiment qualitatively illustrates ozone'.; role in blockinr! harmful. 220-3Wnm wavckmzthi radiation r4.. . . I t also raises the question of whether sunscreen producers are intentionally unconcerned with the W region covered by ozone or if a suitable formulation that encompasses that region has not been found.
-
Caution Ozone is highly toxic (5).Care should be taken that this experiment is done in a well-ventilated area. Literature Cited Figure 1. (a)Position of Tesla coil within permanently sealed cell. (b) Position of Tesla mil in cell with removable windows.
1. Hqylin, M., Ed. Chem. En& News 1991.69 (47). 14. 2. Ra1off.J. Sei. News 1992,141 (l),5. 3. Zurndahl, S. Chemistry. 2nd ed.: D. C. Heath: Lexington, MA, 1989; p 870. 4.Manahsn.S. E.Enuimnmnto1 Chemistry, 5th ed.; Lzwis: Chelsea, MI, 1991: p 347. 5. OSHRs ToxieSubstanees List;29 CFR 19101900 TABLE Z-l-A. 1990.
Volume 71 Number 1 January 1994
83
