Total suspended particulates (TSPs) are particles in the air ranging in size from 10 microns on down to less than a micron in diameter (a micron is one millionth of a meter). People can breathe in many TSPs, though larger particles can be weeded out by such things as nose hairs and mucous membranes. TSPs either result from primary sources (e.g., car exhaust, smokestacks) or are formed from secondary sources, such as ammonia and sulfur dioxide combining to form new pollutants (in this case, ammonium sulfate).