Solubilisation of aerosol trace metals by cloud processing: A laboratory study
- Univ. of East Anglia, Norwich (United Kingdom)
The atmosphere has now been recognized as a major source of both trace metals and nutrients to the oceans, with wet deposition being a major contributor to the flux. Solution pH has been suggested to be the major control on metal solubility in rainwater, but for many trace metals this relationship is not a simple one. Aerosols are typically exposed to [approximately]10 condensation/evaporation cloud cycles before removal in rain and, as a result of H[sub 2]SO[sub 4] and HNO[sub 3] uptake and SO[sub 2] oxidation, cloudwater pH can be very low. Laboratory studies have been conducted, using Saharan and Urban aerosols, to assess the effect of pH on trace metal solubility. The results for the crustal elements Al and Fe in the Saharan aerosol show that metal solubility is a strong function of pH with highest solubilities seen under low pH conditions, comparable to those found in clouds. Increasing the pH to simulate neutralization of acidity by ammonia and crustal material results in almost complete removal of these elements from the solution phase, suggesting that a simple relationship between pH and solubility should exist in rainwater. For Al and Fe in the Urban aerosol there is evidence that some of the material solubilized at low pH is kept in solution at high pH, perhaps as the result of complexation by organic matter. Manganese shows high solubility after the initial acidification from both the Saharan and Urban materials with only slight removal from solution at increased pH. For this element it appears, therefore, that the pH-dependent dissolution process is not reversible. It is tentatively suggested that Fe in the Urban aerosol, under these experimental conditions, is under solubility control.
- OSTI ID:
- 7065293
- Journal Information:
- Geochimica et Cosmochimica Acta; (United States), Vol. 58:15; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ALUMINIUM
DISSOLUTION
CLOUDS
PH VALUE
IRON
MANGANESE
BENCH-SCALE EXPERIMENTS
NITRIC ACID
SULFUR DIOXIDE
SULFURIC ACID
CHALCOGENIDES
ELEMENTS
HYDROGEN COMPOUNDS
INORGANIC ACIDS
METALS
OXIDES
OXYGEN COMPOUNDS
SULFUR COMPOUNDS
SULFUR OXIDES
TRANSITION ELEMENTS
540120* - Environment
Atmospheric- Chemicals Monitoring & Transport- (1990-)