The fractional solubility of aluminium from mineral aerosols collected in Hawaii and implications for atmospheric deposition of biogeochemically important trace elements

The partial solubility of mineral aerosols collected on the windward side of Oahu, Hawaii, was determined by suspending aerosol laden filters in samples of filtered surface seawater and determining the amount of dissolved Al released over a period of four days. The results showed that 80% of the dissolvable Al was released rapidly, within the first 24 h, and that a further 20% was released slowly over the next three days. The mass-based fractional solubility varied from 0.087–14.3% with a mean value of 4.6%.The total dissolvable Al (1st plus 2nd mode) was well correlated with the total charge of nitrate and non seasalt sulphate (nss) (R2 = 0.78, R2 = 0.84) on replicate filters. These results imply that the abundance of atmospheric acids (derived from nitrate and sulphur species) in the atmosphere appears to be one of the major factors controlling the fractional solubility of atmospheric dust in this region. In addition, the results indicate that as this field of study develops there is an urgent need to develop a consensus on the matrix used for defining the solubility of dusts and the development of protocols that eliminate artefacts associated with the determining solubilities that will permit comparison of data between different research groups working in different regions.