Studying Ozone and Air QualityStudying Ozone and Air Quality

Deborah CarlisleDeborah CarlisleSteve SchneiderSteve Schneider

Measuring Ground-level OzoneO3 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 O3

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 PapersOzone 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 are a variety of recommendations for moistening the strips prior to exposure.

Control low O3 high O3

exposure exposure

Despite the method's early limitations, starting in the mid-1800s, 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+

100ppb70ppb

Cntrl

How do Ozone Test Strips Work?Ozone is a strong oxidizer. It rapidly reacts Ozone is a strong oxidizer. It rapidly reacts with the iodide ion, Iwith the iodide ion, I-- in the KI salt applied to in the KI salt applied to the filter paper:the filter paper: KI + H2O + O3 I2 + O2 + K+

I2 + I- + starch I3- + starch (turns blue)

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

Comparing Test Strips

ColorationWhy and How??Why and How?? KI + H2O + O3 I2 + O2 + K+

I2 + I- + starch I3- + starch (turns blue)

Last step : I3- (linear)+ starch (helix)

Combination of I3- and helix

causes light reflection to be in the blue/violet range of visible spectrum

100ppb70ppb

Cntrl

How do Ozone Test Strips Work?Ozone is a strong oxidizer. It rapidly reacts Ozone is a strong oxidizer. It rapidly reacts with the iodide ion, Iwith the iodide ion, I-- in the KI salt applied to in the KI salt applied to the filter paper:the filter paper: KI + H2O + O3 I2 + O2 + K+

I2 + I- + starch I3- + starch (turns blue)

Calibration of Test Strips

Control vs Exposed

Comparing to color scale

Accurate comparison