Water soluble ions of atmospheric aerosols in three New Zealand cities: seasonal changes and sources

The results of one yearʹs measurements (typically a two week sampling campaign in each season) of the concentrations of eight major water soluble ions, namely Na+, NH4+, K+, Mg2+, Ca2+, Cl−, NO3− and SO42−, in atmospheric aerosols collected in three New Zealand cities (Auckland, Christchurch and Hamilton) are presented. The data has provided important information on particulate soluble ion profiles in New Zealand urban areas and revealed some useful trends. A significant correlation has been found between the average meteorological conditions in a sampling campaign and the average particulate concentrations of some of these soluble ions in the campaign. For example, average particulate NO3− concentration in a campaign was found to correlate well with the average calm or weak wind duration percentage in the campaign, and the average concentrations of Na+, Mg2+ and Cl− related closely to the average wind pattern and rainfall in the campaign. Significant site and seasonal variations have been observed with Hamilton having the lowest overall concentrations of all the soluble ions in the particles sampled. On average all sites had the highest particulate concentrations of Na+, Mg2+ and Cl− in the summer but the highest particulate concentrations of NH4+ and non-sea-salt Ca2+ (nss-Ca2+) in the winter. The possible sources of PM10 mass have been deduced and in particular the relative contribution of sea salts to PM10 mass in the cities are reported.