(1) Fine liquid or solid particles such as dust, smoke, mist, fumes, or smog, found in air or emissions. (2) Very small solids suspended in water; they can vary in size, shape, density and electrical charge and can be gathered together by coagulation and flocculation. Flocculation: Process by which clumps of solids in water or sewage aggregate through biological or chemical action so they can be separated from water or sewage