Abstract
Abstract. Acidification of dust aerosols may increase aerosol iron (Fe) solubility, which is linked to mineral properties. Combustion aerosols can also elevate aerosol iron solubility when aerosol loading is low. Here, we use an atmospheric chemical transport model to investigate the deposition of filterable iron and its response to changes in anthropogenic emissions of both combustion aerosols and precursor gases. By introducing three classes of iron-containing minerals into the detailed aerosol chemistry model, we provide a theoretical examination of the effects of different dissolution behaviors on the acid mobilization of iron. Comparisons of modeled Fe dissolution curves with the measured dissolution rates for African, east Asian, and Australian dust samples show overall good agreement under acidic conditions. The improved treatment of Fe in mineral dust and its dissolution scheme results in reasonable predictive capability for iron solubility over the oceans in the Northern Hemisphere. Our model results suggest that the improvement of air quality projected in the future will lead to a decrease of the filterable iron deposition from iron-containing mineral dust to the eastern North Pacific due to less acidification in Asian dust, which is mainly associated with the reduction of nitrogen oxides (NOx) emissions. These results could have important implications for iron fertilization of phytoplankton growth, and highlight the necessity of improving the process-based quantitative understanding of the response of the chemical modification in iron-containing minerals to environmental changes.
Highlights
Bioavailable iron (Fe) is an essential nutrient for primary production in marine ecosystems
The scavenging efficiency of dust particles depends on the surface coating of these aerosols by sulfate, nitrate and ammonium
Filterable iron in dust was released in solution, based on the reactivity of different types of iron associated with mineral properties as a function of aerosol acidity
Summary
Bioavailable iron (Fe) is an essential nutrient for primary production in marine ecosystems. Mineral dust and combustion aerosols are a key external source of bioavailable iron to surface waters in open oceans (Raiswell and Canfield, 2012; Schulz et al, 2012). Modeling studies have examined the impact of land-use change, climate change and CO2 increases on future dust deposition, but future impacts of environmental changes in air quality on bioavailable iron inputs to oceans have not been considered (Mahowald et al, 2009). The measurements for potentially bioavailable iron are commonly made following filtration through 0.2 or 0.45 μm filters. We use the term “filterable” iron here for potentially bioavailable iron in all sizes of mineral dust passing the filters in order to emphasize that this fraction includes ferrihydrite colloids, nanoparticles and aqueous species (Raiswell and Canfield, 2012). The dissolved iron fraction (i.e., the fraction of total aerosol iron that passes through 0.025 μm filters) of iron oxides increases and can approach
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