Impurity sources Of F⁻, Cl⁻, NO₃⁻ and SO₄²⁻ in Greenland and Antarctic precipitation

Five polar impurity sources are proposed: anthropogenic NO 3 − and SO 4 2− in recent Greenland but not Antarctic snow; marine aerosols, the dominant Cl − source; volcanic eruptions, which produce detectable but variable peaks in SO 4 2− , F − , and/or Cl − concentrations; biogenic sulfurous gases from soil and coastal waters, the dominant source for SO 4 2− in nonvolcanic strata; an unidentified source of background nitrate which is more active in the northern hemisphere and which displays a summer concentration maximum. Solar activity and supernova events do not modulate NO 3 − concentrations in Greenland snow.