Earth’s atmosphere contains tiny liquid and solid particles called aerosols. Natural aerosol particles, such as dust and sea salt, tend to be larger than human-produced aerosols, such as particle pollution from burning fossil fuels. These aerosol size maps are based on data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite. Green areas show where the aerosols that were present were mostly larger particles. Red areas show where aerosols consisted mostly of small particles. Yellow areas show plumes with an even mix of small and large particles. Gray shows where the sensor did not collect data.
The snow cover map shows the fraction of an area covered by snow on a monthly basis. Measurements were made by the MODIS sensor on NASA's Terra satellite. Gray indicates land areas with no snow, darkest blue represents minimal snow cover, and solid white indicates 100 percent snow cover. Because MODIS relies on visible light to assess snow cover, the sensor cannot collect data over the highest latitudes of the Northern Hemisphere during winter when no sunlight reaches the polar region.