Scientists use data from NASA’s Total Ozone Mapping Spectrometer (TOMS) to measure the relative amount of aerosols—solid or liquid particles suspended in the atmosphere. Aerosol types detected by the TOMS Aerosol Index include desert dust, smoke and volcanic ash located at least 2 km (1.2 miles) above the surface.Every day, TOMS measures how much UV radiation is absorbed within the atmosphere and how much is reflected back up into space. These measures directly relate to how much aerosol is concentrated within a particular column of atmosphere. Over time, these daily data are combined into a series of 1-month global composite images, such as the false-color image provided above. Brown pixels represent high aerosol concentrations, yellow pixels show lower aerosol concentrations, and light blue regions indicate little or no aerosol present above 2 km in altitude.The Aerosol Index is particularly useful for tracking dust and smoke over bright surfaces, such as deserts or snow- and ice-covered surfaces where other satellite techniques become unreliable. The TOMS Aerosol Index also has the unique capability of seeing smoke and dust when they are above or in the presence of some clouds. (Visit the <a href="http://toms.gsfc.nasa.gov/">TOMS Web site</a> for more details.) Sensor: TOMS/TOMS. Data Start Date: 1/1/91. Data End Date: 7/31/05.