Aerosol Frost flower vs Sea Salt Concentrations with the use of δ34S at Alert, Nunavut, Canada

Frost flowers have been determined to be of significant importance to the sodium content of snow pack and ice cores in costal polar regions. Frost flowers are characterised by a negative dependence of calculated non sea salt sulfate (NSS SO₄^2-) with sodium concentrations in which the calculated NSS SO₄^2- will be less than zero. This negative calculated concentration is because of the frost flower Na:SO₄^2- ratio being larger than that of sea salt ratios. The use of only concentration analysis to determine the presence of frost flower in aerosols does have weaknesses. A negative NSS SO₄^2- concentration will reveal that frost flowers are present but not necessarily how much. For instance, all sodium present may come from frost flowers or only a portion with the remainder coming from sea salt. Samples without negative NSS SO₄^2- concentration may also have frost flower influence to a lesser degree due to excess sulfur coming from anthropogenic influences. This is especially true in the Arctic where Arctic haze from long range transport is prevalent in fall and winter. Unfortunately no clear way has been able to distinguish the amount of sea salt versus frost flower sulfate. A method using stable isotopes is introduced to set limits on the contributions from sea salt and frost flower sulfate. During the Fall of 2007 and 2008, size segregated aerosols were measured biweekly at Alert, Nunavut, Canada for sulfate sulfur isotopes values and major ion concentrations (including sodium and sulfate). Na:SO₄^2- weight ratios ranged from 0 to 9.8. A ratio of 4 would indicate 100% sea salt, with values above 4 indicating frost flower influence and ratios less than 4 indicating other non sea salt sulfate sources (ie. anthropogenic or biogenic). δ³⁴S values ranged between +4 and +15% during the same sampling time period. Explanation of the constraints imposed using δ³⁴S_nss are presented along with the calculation of the maximum and minimum frost flower contribution during the sampling period.