| Popis: |
A new air sampler, the Mist-UV sampling system, has been developed to trap and detect metals and metal compounds present in atmospheric samples, as non-filterable metal (NFM). The Mist-UV system is based on the combination of two ideas, mixing the filtrated air sample with nitric acid mist and simultaneous ultraviolet irradiation of the mist. Atmospheric NFM in the introduced air samples, which were first passed through a 0.2 µm filter, were oxidised by UV irradiation and dissolved in the nitric acid mist. The trapped metals resulting from the NFM in nitric acid were quantitatively determined using ICP-MS. Using the Mist-UV system, measurements of atmospheric NFM concentrations were carried out to obtain their temporal and spatial trends in Auckland, New Zealand. Five metals (Mg, Al, Cu, Ba and Sr) were detected as NFM in ambient air. Elevated atmospheric concentrations of Mg, Cu, and Ba were detected in midsummer and in daytime samples. The UV oxidisable fraction dominated the NFM and high enrichment factors (EFcrust) were found for these metals. This suggested that natural emissions of organometals or reduced metals were responsible for the elevated atmospheric concentrations. Meteorological factors, particularly air temperature, light irradiation and rainfall, promoted biogenic activity and resultant NFM emissions. Remarkably high concentrations of Al and Sr as NFM were discovered in several air samples and were dominated by the non-oxidisable compounds. This implies that the sources of Al and Sr were mainly from inorganic or oxidised metals associated with fine particulates. Wet and dry soils appeared to be the sources of Mg+Ba and Al+Sr, respectively. Plant emissions are recognised as important sources of Mg, Cu and Ba as NFM in ambient air, whereas the suspension of fine particulates derived from road dust and soil enriched with non-oxidisable compounds are seen as the major sources of Al and Sr. The emissions from automobiles and seawater samples were found to be unimportant NFM sources. The NFM concentrations were found to be significantly higher than concentrations of particulate metals, therefore the atmospheric importance and role of NFM cannot be ignored in the estimation of global metal circulation and budgets. |
