Depending on available resources, you may use different sampling materials, or use similar materials but pursue differing methodologies. Overall, each investigation will follow the same basic approach outlined below:
- Define the sampling objective: Describe the scientific question (hypothesis) the project is addressing. For example, if students are concerned about the pollutant levels near their school, the sampling objective might be:
- If pollutants are present and measured on the EPA AirNow web site, the EcoBadge OR ACCESS system OR Ozone Detector Badge OR chemical testing paper OR rubber bands OR milkweed will detect the presence of ozone.
- Due to cool, cloudy, windy weather conditions, and limited sources of NOx, VOCs and PM in the city or town upwind, we predict AQI levels will be low (AQI of 0 - 50).
- If ozone and particulate matter are present outside, we predict measurements will be higher outside than inside of the school, when the windows are closed and measurements are not taken near copy machines or other potential indoor sources of ozone or particulate matter.
- If ozone and particulate matter are present outside, we predict measurements will be roughly equal inside and outside of the school, when the windows are closed and measurements are not taken near copy machines or other potential indoor sources of ozone or particulate matter.
- The NOx, VOCs and PM measurements taken near a school bus that has not been retrofitted will be significantly greater than NOx, VOCs and PM measurements taken near a school bus that has been retrofitted.
- List the sampling parameters: In addition to ozone and particulate matter, each group needs to measure or obtain meteorological parameters including: temperature, relative humidity, wind direction and wind speed. If students are using the ACCESS system, meteorological data is measured by the system. Some schools might have on-site weather monitors that can be utilized. Otherwise, weather data can be obtained by accessing the Weather Underground.
- Describe the method of data collection: Describe where the sampling equipment will be located, how long you will perform sampling, and whether the measurements (experiment) will be repeated in the same day.
- Hints: If you are using the Ozone Detector Badge, a group may want to take five 10-minute readings during the class period and then "average" the results. Or, the students could take a measurement once per hour during the school day to see how the levels compare with the readings on the AIRNow web site, if available in your area.
Ozone is an odorless, colorless gas composed of three oxygen atoms. It is not usually emitted directly into the air, but at ground level it is created by a chemical reaction between oxides of nitrogen (NOx) and volatile organic compounds (VOCs) in the presence of heat and sunlight. Motor vehicle exhaust and industrial emissions, gasoline vapors, and chemical solvents are some of the major sources of NOx and VOCs that help to form ozone. Other sources of VOCs include household products such as paints, paint strippers, and other solvents; wood preservatives; aerosol sprays; cleansers and disinfectants; moth repellents and air fresheners; stored fuels and automotive products; hobby supplies; dry-cleaned clothing.
VOCs + NOx + Sunlight = Ozone
Sunlight and hot weather can cause ground level ozone to form in harmful concentrations in the air. As a result, it is known as a summertime air pollutant. Many urban areas tend to have high levels of ground level ozone, but even rural areas are subject to increased ozone levels because the wind can carry, or transports, ozone and pollutants that form it hundreds of miles away from their original sources.
Measuring ozone can be tricky and yield unexpected results. For instance, urban areas often have lower levels of ozone than adjoining suburban areas because of "ozone scavenging". Ozone scavenging occurs in locations where higher levels of NOx are found, e.g. urban areas or busy highways, due to emissions. In these areas, emissions containing NOx (Nitrogen oxide), react very quickly with O3 (ozone) to form NO2 (Nitrogen dioxide) and O2 (oxygen).
NOx + O3 -> NO2 + O2
This creates overall lower levels of ozone in the urban areas.
The NOx that does not "scavenge" ozone will continue to drift downwind (about 10 - 40 miles), eventually combine with VOCs and react in the sun to produce ground level ozone creating overall high levels of ground level ozone in the downwind location.
In summary, concentrations of ground level ozone tend to be reduced in urban areas due to ozone scavenging, but during ozone episodes, ozone concentrations can be high in areas 10-40 miles away due to wind transport. All of this may cause the ozone levels you measure to be lower or higher than you might expect.
Further, the EPA created air quality standards that limit the levels of ground level ozone in the air to protect public health. There are two standards; a one hour standard (120 ppb) and an eight hour standard (80 ppb). Every area of the country is eventually expected to meet or be below the standards. If an area does not meet, or "attain" the standard, it is considered a "non-attainment" area, and is subject to many more regulations to help make it an "attainment" area in the future.
Measurements are taken by the EPA to ensure the air quality standards are being met. The measurements you will be doing may not be taken at the same time intervals, or the level of precision as the EPA (or state) measurements. Therefore your measurements cannot be directly compared to the AirNow data, nor will you be able to calculate possible exceedences of the one hour or eight hour standard.