Studying Ozone and Air Quality Deborah Carlisle Steve
Studying Ozone and Air Quality Deborah Carlisle Steve Schneider
Measuring Ground-level Ozone O 3 levels above 120 ppb are considered unhealthy. They can be generated by some electrical equipment or from photochemical reactions with smog: VOC’s + NOX + sunlight O 3 Motor vehicles are the single largest contributor to ground-level ozone. In this project we are adapting the relatively easy -to-make Schoenbein papers for classroom use, and using ADI to analyze the color changes quantitatively.
Ozone Levels
Schoenbein Papers Ozone was discovered by C. F. Schoenbein in 1839. He developed an ozone-sensitive test paper that was widely used historically, and more recently in classrooms. The standard protocol for using the papers calls for an 8 -hour exposure to the air out of direct sunlight. Various studies have shown a dependence on humidity, and there a variety of recommendations for moistening the strips prior to exposure. Control low O 3 exposure high O 3 exposure
Historically Despite the method's early limitations, starting in the mid-1800 s, more than 300 stations recorded ozone exposures in countries such as Austria, Australia, Belgium, England, France, Germany, Russia, and the United States.
Schoenbein Papers Cntrl 80 100 120 140+
How do Ozone Test Strips Work? Ozone is a strong oxidizer. It rapidly reacts with the iodide ion, I- in the KI salt applied to the filter paper: KI + H 2 O + O 3 I 2 + O 2 + K+ I 2 + I- + starch I 3 - + starch (turns blue) Cntrl 70 ppb 100 ppb
Facilitating Classroom Use: 1. We find that strips can be exposed dry, stored, and then dipped into water just before photographing. The exposed strips react with the water to produce a more uniform and consistent color that appears less dependent on humidity. 2. With digital monitoring devices, we are developing a digital color scale that can be used to test ozone levels after exposures of only two hours. 3. We are also testing and developing digital color calibration for commercial ozone-testing papers, although their cost per test may be prohibitive for many schools.
Outdoor exposure
Outdoor exposure
http: //www. weather. gov/aq/sectors/nemetro. php#ta bs http: //www. airnow. gov/
Comparing Test Strips
Coloration Why and How? ? KI + H 2 O + O 3 I 2 + O 2 + K+ I 2 + I- + starch I 3 - + starch (turns blue) Last step : I 3 - (linear)+ starch (helix) Combination of I 3 - and helix causes light reflection to be in the blue/violet range of visible spectrum
How do Ozone Test Strips Work? Ozone is a strong oxidizer. It rapidly reacts with the iodide ion, I- in the KI salt applied to the filter paper: KI + H 2 O + O 3 I 2 + O 2 + K+ I 2 + I- + starch I 3 - + starch (turns blue) Cntrl 70 ppb 100 ppb
Calibration of Test Strips
Control vs Exposed
Comparing to color scale
Accurate comparison
- Slides: 20