Clean corona gas ionization by separating contaminant byproducts from corona generated ions includes establishing a non-ionized gas stream having a pressure and flowing in a downstream direction, establishing a plasma region of ions and contaminant byproducts in which the pressure is sufficiently lower than the pressure of the non-ionized gas stream to prevent at least a substantial portion of the byproducts from migrating into the non-ionized gas stream, and applying an electric field to the plasma region sufficient to induce at least a substantial portion of the ions to migrate into the non-ionized gas stream.