AIR & THE
Activity 11 (Explore): Measuring Wet Deposition
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In this multi-day activity, students collect data to test the accuracy of one portion of their Chesapeake Bay Pollution models. The activity is written for students to collect and analyze rainwater to see if the air has nitrate or ammonium pollution in it. Since MWEEs are designed to be student-driven, this experiment can be modified to test other aspects of their models as well, including water from nearby streams or from the Chesapeake Bay itself.
Student Choice & MWEEs: MWEEs are designed to promote student choice, especially when it comes to the experimentation, field experiences, and data collection. What is presented here is one option for what students might do to collect data related to air pollution. Others might include collecting water from a local stream and testing for nitrates and ammonium (from runoff pollution), participating in a field experience with a partner organization to collect nitrate data from the Bay, or devising their own method for collecting emissions data from (for example) car exhaust. The important thing is to focus on the type of pollution that is local for students. For many students in the DC-Baltimore area, that pollution is air pollution from transportation.
Activity Objectives & Materials
Approximate Time: 2-3 class periods (120-180 minutes)
Students will collect and analyze data to determine if rainwater in the school community is polluted with nitrogen
Nitrate and ammonia test kits (see note on materials)
Additional glassware (ex. small beakers) to allow for multiple groups to test at the same time if necessary
Rainwater collectors (ex. jars)
Distilled water (to use as a control)
Safety & cleanup materials (safety goggles, paper towels, etc.)
Tips for Measuring Nitrogen Deposition in Rainwater (teacher guide)
Nitrogen Deposition in Rainwater
A Note About Timing for This Activity: This activity requires collecting rainwater from the school grounds. Since precipitation can be an unpredictable occurrence, consider having students make and put out their rainwater collectors as early as possible so that you have rainwater to use. The amount of nitrate and ammonium in the water will decrease if it is not tested soon after the rainfall, but they can be frozen and thawed without significantly affecting the nitrate and ammonium concentrations. Steps 1-4 of the activity introduce the experiment up through making rain gauges, and the remaining steps include water testing, data analysis, and conclusions.
A Note About Materials for This Activity: The amount of nitrate and ammonium in rainwater is relatively low, so sensitive tests are required to detect it. There are several companies that produce easy-to-use nitrate and ammonia water tests that are sensitive enough. Kits from CheMetrics are recommended because they are relatively inexpensive and very easy to use. To limit costs, you may consider using one test instead of both. In that case, the Nitrate kit is recommended because it is often present in higher amounts and so will be easier to detect. Refill kits are also less expensive, so if you use the kit in subsequent years, you only need to buy the refills.
Hach also produces similar test kits which are slightly more expensive, but which also have the required sensitivity.
DCI: LS2.C: Ecosystem Dynamics, Functioning, and Resilience
DCI: ESS3.C: Human Impacts on Earth Systems
SEP: Planning & Carrying Out Investigations, Creating & Using Models, Constructing Explanations
CCC: Cause & Effect
How does nitrogen pollution get into rainwater?
When nitrogen pollution in gas form (NOx) is released into the atmosphere, it dissolves into the water in clouds and rain.
This warmup is designed as a reminder to make sure students understand why they are collecting and analyzing rainwater
1. Frame the Activity
Tell students that when scientists create models to explain something, they also need to test the model to see if it’s accurate. While the students cannot test their whole model, they can test part of it to see if what they believe is supported by data. For example, they could test water in local streams to see if it has nitrate in it from wet deposition, or they can test water near farms to see if it has ammonium in it from fertilizer and manure washing off the land. Tell students that there is one type of nitrogen pollution they can test anywhere in the airshed, even if they are not near a stream or a farm. Ask students if they know what kind of pollution they can test for no matter where they are. Use questions to help them realize they can test rainwater to see if the air has nitrogen pollution in it. Ask students if they think the rainwater in their community is polluted. Tell them that they are going to perform the same experiments that scientists do in order to see whether there is wet deposition of nitrogen in their part of the Chesapeake watershed.
2. Develop a Research Question
Tell students that they will be testing rainwater for nitrate and/or ammonium using a chemical test kit. Before they do that, they need to write a research question based on their model. The research question should ask something about nitrogen pollution in rainwater. Help students to develop a research question related to testing nitrate and/or ammonium levels in rainwater. For example:
Does rainwater in our community have higher levels of nitrate than plain water?
Is the amount of ammonium in rainwater that falls in our community higher than it plain water?
Hand out the Nitrogen Deposition in Rainwater sheet to students and have them write down their research question.
3. Develop a Hypothesis
Ask students what results they expect from their experiment based on their model of Chesapeake Bay pollution. Because students have not discussed actual concentration numbers, their hypotheses can be general (ex. I think that there will not be any nitrate in the rainwater because the air in our community is very clean). Have them write their hypothesis on their handout.
4. Make Rain Gauges
Lead students through the process of creating rain gauges to collect water for their experiment. See the section of the teacher guide under “rainwater collection” for ideas about making and setting up the gauges. When they are ready, set the gauges out around the school grounds (some students may set them up at home) in safe locations.
Modification: If performing the experiments yourself is not possible due to cost constraints or other circumstances, you can have students review data from the National Atmospheric Deposition Program instead. While this is far from ideal, it will allow students to be able to see what the nitrate and ammonium concentrations are like in the rainwater in their area. See Step 9 for how to access these data.
5. Review Testing Procedures
Continue here after rainwater has been collected and is ready to test.
Hand out copies of the nitrate and ammonia testing procedures to students. Review the directions for the procedures, and make sure to discuss with students why they need to test distilled water as well as the rainwater. You may want to complete one test as an example for students or have all students do each step together.
6. Conduct the Tests
Have students take rainwater (either from their jars, or from rainwater that has been frozen and thawed) and distilled water, and complete the tests to determine the amount of nitrate or ammonium in each sample. Make sure students know where to record their data on their data sheets. Be sure to follow safety procedures and clean-up all materials appropriately.
Control Group: The ideal control group for this experiment would be unpolluted rainwater. However, this is nearly impossible to obtain, so distilled water has been substituted. For information on the composition of unpolluted rainwater, see this website.
7. Pool Data
As students complete their experiments, have them share their data with the rest of the class, either using the board or a computer. Make sure that students record the data in the correct place on their data sheets (ex. nitrate control/experimental; ammonia control/experimental). When they have all the class data, have them calculate averages for each of the tests and write the averages on their data sheets.
8. Convert Units
Scientists report out the amount of nitrogen in rainwater samples as concentrations of nitrate (ppm NO3) and ammonium (ppm NH4). However, most test kits report out on the concentration of nitrogen itself (ppm N-NO3 and ppm N-NH4). As such, students need to convert from one unit to the other in order to compare their data with data collected by scientists. The conversion is simple: multiply by 4.43 to convert from ppm N-NO3 to ppm NO3 and multiply by 1.29 to convert from ppm N-NH4 to ppm NH4. Review this information with students to the degree that they will understand it, and have them complete the conversions on their data sheets.
9. Comparing with Official Data (optional)
Data collection stations around the country follow similar procedures to collect nitrate and ammonium wet deposition data. Go to the National Atmospheric Deposition Program website to find these data. Choose the interactive map option to find the weather station closest to you. Blue pins on the map show active sites. Click on the pin closest to the school to bring up information about that site.
From the popup menu, click the Data Access link and then the Data tab to see what information is available. Here is a list of commonly available site data:
Weekly data (week-by-week deposition data in excel format)
Trend plots (graph of average deposition on an annual basis)
Annual averages (annual average concentrations in excel format)
Precipitation (rainfall timing and amount in excel format)
The trend plot is easy to read and will allow you to compare your results with annual averages and trends. The weekly data will allow you to see how your data falls into the range of common concentrations. Unfortunately, there is a significant time delay for the national data to be posted, so you cannot get comparison information for recent rainfall events like the one your data come from. Use the link for “metadata” to learn what each of the columns in the spreadsheets represents.
10. Data Analysis
The data from the rainwater testing will likely be very straightforward since the test kits do not have extremely precise measurements, and student data is unlikely to have much variation. Unless there is significant variation among student results, students should graph the results of their class averages from each of the tests done (including control groups). Have students write a simple analysis of the data in the space on their data sheets (ex. the difference between the experimental and control group concentrations, and whether it was higher or lower).
11. Formative Assessment: Conclusion
Have students write a conclusion to their experiment by answering the Claim-Evidence-Reasoning prompt. You may want to discuss conclusions beforehand to help students with their writing. Also consider using one or more of the scaffolding techniques in the differentiation note – or use another technique of your own.
Differentiation: If students are new to the CER writing format, consider ways to scaffold the writing prompt. For example, you can have student groups work together to write the CER, or just one part of it. You can also have students write drafts of the reasoning portion, review them together to provide feedback, and have students complete a final draft afterwards.
Modification: Because this experiment follows a traditional format, you may want to have students write up their results using a scientific paper format that includes the scientific question, hypothesis, methods, results and conclusion. Middle school students will likely require significant support and scaffolding with this format as it is likely new to them.