Spinning dust grains in front of the bright Galactic synchrotron background can produce a weak absorption signal that could affect measurements of high–redshift 21 cm absorption . At frequencies near 80 MHz where the Experiment to Detect the Global EoR Signature ( EDGES ) experiment has reported 21 cm absorption at z \approx 17 , absorption could be produced by interstellar nanoparticles with radii a \approx 50 { \AA } in the cold interstellar medium ( ISM ) , with rotational temperature T \approx 50 K. Atmospheric aerosols could contribute additional absorption . The strength of the absorption depends on the abundance of such grains and on their dipole moments , which are uncertain . The breadth of the absorption spectrum of spinning dust limits its possible impact on measurement of a relatively narrow 21 cm absorption feature .