Seasonal variations in the atmospheric concentration of non-filterable metals (NFM) and possible emission sources

Seasonal variations in the atmospheric concentrations of non-filterable metals (NFM) have been observed using a newly developed Mist-UV sampling system in Auckland, New Zealand. We define NFM as volatile metal compounds and metal compounds in the nucleation and accumulation modes (<0.2 μm). Fifty-seven NFM samples were collected between September 2000 and August 2001, and five metals (Mg, Al, Cu, Sr and Ba) were detected in most samples during the campaign. Elevated atmospheric concentrations of Mg, Cu, Sr and Ba were detected in midsummer. Since the UV-oxidisable fraction was dominant, and high enrichment factors (EFcrust) were found for these metals, it is suggested that natural emission of organometals or reduced metals, were responsible for the high concentrations observed. Several elevated concentrations of Al and Sr as NFM were discovered in their annual profiles and these are attributed mainly to inorganic or oxidised metals associated with ultra-fine particulates. In summer Mg, Cu, Sr and Ba as NFM concentrations were 3–15 times higher than when associated with particulate matter (PM10). The emissions from automobile and seawater samples do not appear to be NFM emission sources, however, wet soils and dry soils were probably the sources of Mg+Ba and Al+Sr, respectively. Overall it is believed that metals released by natural sources were responsible for at least some of the metals detected, although a contribution from urban sources is possible. Our observations imply that atmospheric volatile and ultra-fine particulate metals cannot be ignored in the estimation of global metal circulation and budgets.