Part 3—Explore Population and Pollution in Phoenix, AZ

Step 1 Examine Population and NO2 Concentration in Phoenix, Arizona

  1. Under the Search panel on the left, type Phoenix, AZ into the "Fly to" field, then press return (or enter) on your keyboard.
  2. Use the transparency bar to view the Population Density and January 2010 NO2 data layers.
    • Do the data in this close-up view of Phoenix fit your previous observations about population density and NO2 concentrations?
      Yes. Both population density and NO2 concentration are high in the Phoenix area.
  3. Deselect the checkboxes to turn both data layers off.

Step 2 Explore the Geography of Phoenix, AZ

An oblique view of Phoenix, Arizona generated by Google Earth.
  1. Under the Layers heading near the bottom of the panel on the left of the Google Earth window, check the box for the Terrain layer. This will produce a three-dimensional visualization of topography. Though the time it takes for redrawing each scene is longer, the visual effect is worthwhile.
  2. Zoom in to downtown Phoenix. Adjust the zoom to get an Eye Alt of around 1.5 to 2 km (1 mile). Read the "Eye alt" value shown in the extreme lower right of the Google Earth window.
  3. Tilt the view forward to display an oblique (at an angle) view of Phoenix. You may have to wait for the display to show a three-dimensional view of the terrain.
    Click the up or down arrows of the Look joystick to tilt the image.


    For more information on the navigation controls in the version of Google Earth that you are using, go to Help > User Guide from within Google Earth.
  4. Using the Rotate function, rotate your view to look in all directions. The visualization is similar to standing on a tall building in Phoenix and looking all around you.
    This image shows the rotate controls in Google Earth. Click and drag the N around the outer circle in either direction.


    • Describe the geography of the Phoenix area. What is the shape of the land where the city's homes and buildings are? What features surround the metropolitan area?
      Answers will vary. In general the city itself is on flat land, while there are mountains surrounding it on three sides.

Step 3 Explore the Relationship between Geography and NO2 Concentration

  1. While in the oblique view, turn on the January 2010 NO2 data layer and adjust the transparency slider so you can see the layer (make it opaque).
  2. Use the Rotate function to look all around again; use the color scale to understand what the visualization is showing.
    • What are the NO2 concentrations like across the city?
    • How does that compare with the NO2 concentrations over the mountains that are visible beyond the Phoenix metropolitan area?
    • The predominate westerly winds push the air pollution towards the mountain ranges to the east of Phoenix. This causes an increase in the concentration of NO2 and other pollution, such as tropospheric ozone and particulates.
  3. In both the oblique view and the map view, use the techniques of turning layers on and off and controlling their transparency to examine the relationship between NO2 concentrations and geography.
    • From your observations of Phoenix, describe your ideas about how geography affects NO2 concentrations.

      Geographic setting appears to influence concentrations of NO2. Topographically high areas (mountains) act as obstacles to air flow: they trap air that contains NO2, keeping it within the Phoenix metropolitan area.



      This graphic shows that NO2 concentrations are high (dark brown) over the flat city and mountains immediately surrounding it. The areas beyond the ring of mountains that surround Phoenix have lower NO2 concentrations.


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