Field Lab 6: UV light and Air Pollution

Last updated 3-16-16

Field Lab 6: UV light & Air Pollution Sunglasses and windows UV Protection Ozone Detection
	Sunlight is good, but there is a saying, "You can get too much of a good thing." Which is quite true regarding the light from the Sun. This is especially true of ultraviolet light, which can break apart the DNA and other molecules in the cells of our skin and eyes.
	What makes light more dangerous is the fact that they lens of the eyes focuses light into a spot point (region) at the back of the eye. So if there is too much of infrared, visible, or ultraviolet light, its concentrated on the point of focus, which can destroy cells.
All of the energy released as the gasoline molecules break up and combine with oxygen creates high pressure of carbon dioxide and water vapor in the engine cylinder. This pressure is used to push the cylinder down and make the car go. After the piston gets pushed down and is heading back upward, the hot gases (CO₂ and H₂O vapors) are released to the exhaust system shown below...
	Sunglasses are a good defense against excess sunlight (and excess UV light). However, even while wearing sunglasses, you can't look directly at the sun because it still is strong enough to burn the back of the eyes (the retina).
	Welding goggles or something made for looking at the Sun are the only recommended ways of looking directly at that sun. Even if the sun looks dark through goggles, it still can be doing damaged via infrared or ultraviolet light which can't be seen. .
	UV protection labels: These sunglasses are labeled "UV 400 protection". This is supposed to mean that it blocks nearly 100% of ultraviolet shorter than 400 nanometers (any longer then it is visible light). However, the "UV 400 Protection" label does not have an official definition. So these may be good or bad.
	UV protection labels: On These sunglasses have the "Polaroid" label. Polaroid lenses only allow light waves that are vibrating in a particular direction. Light (infrared, visible, or ultraviolet) bouncing off the highway, water (pond, lake, ocean), or shiny horizontal surfaces (like hoods of cars) will end up vibrating from side to side (see image). Those waves get blocked by polarized sunglasses. So these glasses reduces reflections off of shiny horizontal surfaces, but they still allow ultraviolet light to come through. So these Polaroid glasses may not be good at protecting eyes from ultraviolet light.
	CE standard: If In Europe sunglasses must meet certain quality standards for blocked out 99% of UVA and UVB light. Plus they must also be shatter resistant. When they pass these tests, they can have a "C E" stamp of approval. These glasses show the CE symbol; however, these glasses are suspected of being fake Gucci glasses. So the CE may be fake, also.
	Dark sunglasses would seem to be good at blocking UV light; however, if sunglasses look dark, it is only because they are blocking visible light. They could be allowing UV light to pass right through. If that is the case, having dark sunglasses will make it worse because the pupils of your eyes will open up wide letting in more damaging UV light.
	Yellow tinted sunglasses are yellow because they block blue light. Since blue light is close to ultraviolet light, then these are likely blocking at least the UV light which is close to blue light (UVA light). However, it doesn't mean it is blocking UVB light, which is more damaging.
	Expensive sunglasses are no guarantee that they have good UV protection. On study showed that $6.95 sunglasses had more protection than sunglasses costing over $100.
	Your could buy a brand such as Ray-Ban that has a reputation of glasses that block UV rays. However, tests show the shape of the sunglasses are just as important. These $225 glasses will allow a lot of UV rays coming around the sides of the glasses.
	The lesson is that it's best to test the sunglasses yourself rather than rely on whatever is written on the sunglasses. It's also best to use wrap-around sunglasses. These beads turn from white to color when exposed to UV light. In this photo, the beads behind the sunglasses should be white if they sunglasses is blocking UV light. Since these have as much color as the beads directly in the sunlight, then the sunglasses are not blocking the UV light.
A) Field Lab 6: Detecting % UV blocked using UV detection beads
	1) To test your sunglasses, use either the UV beads in a plastic bag or a test tube. Have half of the bag (or test tube) sitting behind the sunglasses. The other half should be getting direct sunlight. The beads behind the sunglasses may start out colored because they were exposed to the sunlight before you get them behind the sunglasses. 2) Wait about 2 minutes for any color to fade before you estimated how well your sunglasses are blocking UV light. Also, it's best if you hand can block UV light coming from behind the sunglasses. UV light does bounce off of objects in the background. In this photo, the color of the beads behind the sunglasses seem to be about half as intense (saturated) as the color of the beads being exposed to the sun. So that means the sunglasses are blocking 50% of the UV light. If the color was estimated to be about 1/4 of that of the ones in the sun, then I would say it was blocking 75% of the UV light. A1) Using the amount of color in the beads behind the sunglasses compared to the color of the ones in the sun, estimate the percent of the UV light your sunglasses block. A2) Do the same test with someone else's sunglasses. How much do those sunglasses block? A3) Do the same test with one other person's sunglasses. How much do those sunglasses block?
	3) Now place the bag or test tube of UV beads on the dash of your car with sunlight coming through the windsheild. A4) What percent of UV light does your windshield block? In this picture, the beads seem to half about 1/3 of the color as the beads are when directly in the sun. So I would say the windshield is blocking about 67% of the UV light. It is possible that the windshield is blocking more, but UV light could be coming in from the side and back windows of the car.
	4) Now hold the bag or test tube of UV beads up to the side window of your car where sunlight is hitting the car window (It's OK if you open the car door to get the sun to hit the window more directly). A5) What percent of UV light does a side window in your car block?
	5) Now hold the bag or test tube of UV beads up to a window in your home where sunlight is hitting the window. A6) What percent of UV light does your a window in your home (apartment) block?
B) Field Lab 6: Detecting ozone using ozone test strips
Below were the steps you did in the on-campus lab to make the ozone test strips.

The detection of ozone depends on the below 4 chemical reactions happening on the paper test strip that was dipped into a soluiton of potassium iodide and cornstarch. The first chemical reaction shows that potassium iodide (KI) in contact with moisture in the air plus ozone in the air will form iodine (I₂). The second reaction is potassium iodide reacting with moisture in the air to produce the iodide ion. Next, the iodide ion (I^-) from the 2nd reaction and the iodine (I₂) from the 1st reaction combine to make triiodide ion (I₃^-). Finally, the triiodide ion that got produced because of ozone reacts with the cornstarch (amylose starch) to make a colored triiodide & amylose complex
	When that last reaction occurs, the color change of the cornstarch gives the paper a purplish brown color. The deeper the color, the more ozone was present.
	1) Place one ozone test strip outside where you live. It is best to place it outside in the morning and retrieve it 8 hours later. Anchor it down somehow. I used a rock, but I didn't cover up the part of the strip that had been dipped. Air needs to get to the strip. You can use tape, a paper clip or thumb tack if you want to secure it. But again, place it so air can get to it. 2) Make a note of what time you placed the strip outside. You will need to leave it there for about 8 hours. You will also need to know the humidity. Farther down on this Web page are instructions on how to do that.
	3) Place another ozone test strip inside your house somewhere. Again, it needs to be where the air can flow over it. Also, note what time you placed it. Retrieve it about eight hours later to read the ozone level.
	4) On the same day or a different day where you plan on driving somewhere, place the third strip on your car. Under the wiper blade works well. For example, if you drive to school or work and leave your car parked there all day, that would be good. You are trying to get a total of 8 hours exposure.
To calculate the ozone concentration, you need to know the relative humidity during the day that you had the test strip outside. Below are the instructions of how to find the average humidity for the time the strip was exposed. First go to this site: http://www.weather.gov/ 1) At left of the page, type in your zipcode and click "Go". 2) A new page will appear with the current weather for that zipcode. In the center is the current humidity. 3) At the right of the page is a link titled "3 Day History". Click that link and it will take you to a new page. 4) On the history page is a list that shows the temperature and humidity about every half hour for the last 3 days. Use that to find the humidity at the time you first placed the strip and the humidity at the time you read the strip about 8 hours later. 5) Add the humidity at the time you set the strip out to the humidity at the time you read the strip. Divide that sum by 2 to get the average humidity throughout the day. B1) What is was the average humidity for the day that you placed an ozone test strip outdoors? B2) What is was the average humidity for the day that you placed an ozone test strip indoors? B3) What is was the average humidity for the day that you placed an ozone test strip on your car?
	After leaving the strips exposed to the air for 8 hours, compare their color to the chart at the left (or the one below), and determine the "Schonbein number." Christian Friedrich Schonbein was the discoverer of ozone and gave it its name, meaning "odd smell". He also developed the test for ozone using the ingredients you are using in this lab.
	The above color chart uses colors that are given in the literature, but the strips made with this kit seem to be closer to the color chart to the left. Use whichever one is easier to match.
	Here are my outdoor and indoor ozone test strips. The outdoors clearly has the most ozone. Match the lightest and the darkest colors to the chart above, then pick the number halfway between them. For example, my outside strip has parts that match #5 and dark areas that match #8. Halfway between them is 6.5. So 6.5 is the Schonbein number for that strip. The indoors strip shows maybe a level of 1. If you can, take a picture of the test strips. B4) Using the same approach, what is the Schonbein number for your outdoor ozone test strip? B5) Using the same approach, what is the Schonbein number for your indoor ozone test strip? B6) Using the same approach, what is the Schonbein number for your ozone test strip on your car?
	Locate the Schonbein number on the bottom axis of the graph. In my case, the Schonbein number was 6.5. Come straight up and find the spot that comes the closest to the average humidity during the time you did the test. The average humidity was 32% for me, so it sits between the 30% and 40% lines, but closer to the 30% line. At that point go straight to the left to read the ozone concentration in parts per billion (ppb). The other reading of "1" is done the same way. So in my example, I would say the blue arrow points to about 165. So my outdoors ozone strip indicates the ozone level was 165 ppb (parts per billion). For the indoors strip, I would say the blue arrow points to 42. So in my home the ozone level was 42 parts per billion.
	B7) Using the Schonbein number for the outdoor ozone test strip (x-axis) combined with the average relative humidity (curved lines), what level of ozone in ppb does your test strip indicate outdoors of your home? B8) Using the Schonbein number for the outdoor ozone test strip (x-axis) combined with the average relative humidity (curved lines), what level of ozone in ppb does your test strip indicate inside of your home? B9) Using the Schonbein number for the outdoor ozone test strip (x-axis) combined with the average relative humidity (curved lines), what level of ozone in ppb does your test strip indicate where your car has been?
	The chart on the left lists the health warning for 8 hour exposure to ozone at different ppb (parts per billion). B10) Using the ozone level (ppb) indicated by your outside ozone test strip, what health rating outside your home be according to the chart? B11) Using the ozone level (ppb) indicated by your indoors ozone test strip, what health rating would inside your home be according to the chart? B12) Using the ozone level (ppb) indicated by the ozone test strip on your car, what health rating would being in your car be according to the chart?

Either send your results to chm107@chemistryland.com or print (or write them down) and hand them to Mr. Costello in the lab class.

<-CHM-107 Lab Home Page