Aura's instruments study tropospheric, or low-level atmospheric chemistry and will monitor air pollution around the world on a daily basis. Aura measures five of the six 'Criteria Pollutants' identified by the U.S. Environmental Protection Agency. Note: This animation shows how ozone in the Troposphere changes from September 28, 2004 to November 6, 2004. Areas of Red represent high levels (50+ DU) and areas of blue represent low areas (20 DU). Animator: Lori Perkins (NASA/GSFC), Stuart A. Snodgrass (GST). Scientist: Mark Schoeberl (NASA/GSFC), Ernest Hilsenrath (NASA/GSFC), Jerry Ziemke (NASA/GSFC), Sushil Chandra (NASA/GSFC). Platforms/Sensors/Data Sets: Aura/OMI.