Saharan Dust Transport (Polvo del Sahara)

Estimated Time: 45-60 minutes

Materials: Internet access, Saharan Dust Transport Simulation

Part 1: Engage (Anchoring Phenomenon)

Every year, millions of tons of mineral dust are swept up from the Sahara Desert in Africa and transported thousands of miles across the Atlantic Ocean by the trade winds. This massive plume of dry, dusty air is known as the Saharan Air Layer (SAL). When this dust reaches the Caribbean and places like Puerto Rico, it can drastically reduce air quality, causing severe respiratory issues for residents. However, this same dust layer also suppresses the formation of tropical cyclones (hurricanes) in the Atlantic and deposits critical nutrients like phosphorus and iron into the El Yunque rainforest and marine ecosystems.

Student Task: Consider the phenomenon described above. How can one event—dust blowing off a desert in Africa—cause such different impacts (both positive and negative) across the globe? Write down at least two questions you have about how the dust travels and what factors might influence its journey and impacts. ___ _____ _______

Part 2: Explore (Simulation Investigation)

In this simulation, you will adjust the environmental factors that influence the transport of the Saharan Air Layer (SAL) and observe the resulting impacts on air quality (AQI) in Puerto Rico and the probability of hurricane formation in the Atlantic.

Instructions:

1. Open the Saharan Dust Transport simulation.
2. Locate the three main control sliders:
   • Sahara Dust Emission: Controls the amount of dust lifted into the atmosphere (Low, Medium, High).
   • Trade Wind Speed: Controls the speed of the winds carrying the dust across the ocean (5 to 35 mph).
   • Atlantic Precipitation: Controls the amount of rain over the ocean, which can wash dust out of the air before it reaches the Caribbean.
3. Test out the different sliders. Press the Play button to run the simulation and observe the dust plume moving across the map.
4. Watch the Data Analysis panel on the right. Note the Current AQI (PR) and the Hurricane Prob. metrics.
5. Pause or Reset the simulation as needed. Fill in the data table below by testing the specified combinations. Run each test for at least 15 simulation days to allow the dust to travel.

Data Collection:

Part 3: Explain (Sensemaking)

Use the data you collected to answer the following questions:

1. Emission Impact: Based on your comparison of Test 1 and Test 2, how does increasing the Sahara Dust Emission affect the Air Quality Index (AQI) in Puerto Rico? How does it affect the probability of hurricane formation? ___ _______

2. Wind Speed Impact: Compare Test 2 and Test 3. How did increasing the trade wind speed change the impact of the dust? Why do you think this happens? ___ _______

3. Precipitation Impact: Compare Test 2 and Test 4. What happens to the dust when there is high precipitation over the Atlantic Ocean? How does this change the outcomes for Puerto Rico? ___ _______

4. Feedbacks: The Saharan Air Layer creates a feedback loop with the climate system. Based on your observations, describe the relationship between the presence of the dry, dusty SAL and the formation of tropical cyclones (hurricanes). Does the dust increase or decrease hurricane probability? ___ _______

Part 4: Elaborate/Evaluate (Argumentation & Modeling)

Constructing an Argument: Imagine you are an environmental scientist reporting to the government of Puerto Rico. Some officials are proposing a hypothetical (and impossible) technology to completely block the Saharan trade winds to stop the dust from reaching the island, hoping to permanently solve their air quality problems.

Using the data and concepts from the simulation, write a brief argument explaining why blocking the Saharan dust would have complex and potentially dangerous unintended consequences.

Your argument must:

• State a clear claim about whether blocking the dust is a good idea.
• Provide evidence from the simulation regarding the relationship between the dust layer and hurricane formation.
• Describe the tradeoffs of the dust (e.g., negative impacts on air quality vs. positive impacts on hurricane suppression).

Your Argument: ___ _____ _____ _____ _______

Extensions

• Nutrient Deposition: Research how phosphorus from the Saharan dust impacts the Amazon Rainforest or marine phytoplankton blooms. How does this connect to the carbon cycle?
• Climate Change Connection: Use reliable sources to investigate how changing global temperatures might affect the frequency or intensity of Saharan dust storms in the future, and how that might in turn affect the Atlantic hurricane season.

Teacher Notes

NGSS Alignment

This task is designed to align with the following Next Generation Science Standards (NGSS) Performance Expectation:

HS-ESS2-2: Analyze geoscience data to make the claim that one change to Earth’s surface can create feedbacks that cause changes to other Earth systems.

Evidence Statements Addressed:

• 1. Organizing data: Students organize data that represent measurements of changes in hydrosphere, cryosphere, atmosphere, biosphere, or geosphere in response to a change in Earth’s surface. (Students collect data on AQI and hurricane probability based on changes in dust emission, wind, and precipitation).
• 2. Identifying relationships: Students use tools, technologies, and/or models to analyze the data and identify and describe relationships in the datasets, including:
  • i. The relationships between the changes in one system and changes in another (or within the same) Earth system; (Students identify how dust in the atmosphere changes hurricane formation in the hydrosphere/atmosphere and air quality in the biosphere).
  • ii. Possible feedbacks, including one example of feedback to the climate. (Students identify the feedback loop where the dry SAL suppresses hurricane formation).
• 3. Interpreting data: Students use the analyzed data to describe a mechanism for the feedbacks between two of Earth’s systems and whether the feedback is positive or negative, increasing (destabilizing) or decreasing (stabilizing) the original changes. (Students argue how removing the dust would remove the stabilizing feedback that suppresses hurricanes, potentially destabilizing the region with more frequent storms).

3D Learning Dimensions:

• Science and Engineering Practices (SEP): Analyzing and Interpreting Data.
• Disciplinary Core Ideas (DCI): ESS2.A: Earth Materials and Systems (Earth’s systems, being dynamic and interacting, cause feedback effects that can increase or decrease the original changes). ESS2.D: Weather and Climate.
• Crosscutting Concepts (CCC): Stability and Change (Feedback can stabilize or destabilize a system).