SCAR_A_ER2_MAS data are Sulfates, Clouds and Radiation America (SCARA) NASA ER2 Moderate Resolution Imaging Spectrometer (MODIS) Airborne Simulator (MAS) Data in Hierarchical Data Format (HDF).Smoke/Sulfates, Clouds and Radiation - America (SCAR-A) data include physical and chemical components of the Earth's surface, the atmosphere and the radiation field collected in the eastern part of the United States with an emphasis in air pollution.The primary objective of the SCAR-A experiment was to help scientists characterize the the relationship between sulfate particles and clouds' reflective properties. Sulfate aerosols are believed to provide condensation nuclei, resulting in smaller, more numerous droplets within a cloud. SCAR-A was the first in a series of experiments. It was was followed by the SCAR-C experiment conducted over California in 1994. A third experiment, SCAR-B was conducted in Brazil during August and September 1995. The MODIS Airbourne Simulator (MAS) is a modified Daedalus Wildfire scanning spectrometer which flies on a NASA ER-2 and provides spectral information similar to that provided by the Moderate Resolution Imaging Spectroradiometer (MODIS), launched on Terra (EOS AM-1) in 1999 and Aqua (EOS PM-1) in 2002. The MAS spectrometer acquires high spatial resolution imagery in the wavelength range of 0.55 to 14.3 microns. A total of 50 spectral bands are available in this range, and the digitizer can be configured to collect data from any 12 of these bands. The digitizer was configured with four 10-bit channels and seven 8-bit channels. The MAS spectrometer was mated to a scanner subassembly which collected image data with an IFOV of 2.5 mrad, giving a ground resolution of 50 meters from 20000 meters altitude, and a cross track scan width of 85.92 degrees. The data granules were written using the self documenting file storage format provided through the netCDF interface routines included in the HDF libraries.