This paper presents a review of recently acquired knowledge on the physico-chemical properties of mineral dust from Africa and Asia based on data presented and discussed during the Third International Dust Workshop, held in Leipzig (Germany) in September 2008. <br></br> Various regional field experiments have been conducted in the last few years, mostly close to source regions or after short-range transport. Although significant progress has been made in characterising the regional variability of dust properties close to source regions, in particular the mineralogy of iron and the description of particle shape and mixing state, difficulties remain in estimating the range of variability of those properties within one given source region. As consequence, the impact of these parameters on aerosol properties like optical properties, solubility, hygroscopicity, etc. – determining the dust impact on climate – is only partly understood. Long-term datasets in remote regions such as the dust source regions remain a major desideratum. <br></br> Future work should also focus on the evolution of dust properties during transport. In particular, the prediction of the mineral dust size distribution at emission and their evolution during transport should be considered as a high-priority. <br></br> From the methodological point of view, a critical assessment and standardisation of the experimental and analytical techniques is highly recommended. Techniques to characterize the internal state of mixing of dust particles, particularly with organic material, should be further developed

Acidic air pollutants dissolve iron in aerosols and fertilize the ocean.

No abstract

The chemical history of dust particles in the atmosphere is crucial for assessing their impact on both the Earth's climate and ecosystem. So far, a number of studies have shown that, in the vicinity of strong anthropogenic emission sources, Ca-rich dust particles can be converted into aqueous droplets mainly by the reaction with gaseous HNO 3 to form CaðNO 3 Þ 2 . Here we show that other similar processes have the potential to be activated under typical remote marine atmospheric conditions. Based on field measurements at several sites in East Asia and thermodynamic predictions, we examined the possibility for the formation of two highly soluble calcium salts, CaðNO 3 Þ 2 and CaCl 2 , which can deliquesce at low relative humidity. According to the results, the conversion of insoluble CaCO 3 to CaðNO 3 Þ 2 tends to be dominated over urban and industrialized areas of the Asian continent, where the concentrations of HNO 3 exceed those of HCl (½HNO 3 ∕HCl > ∼1). In this regime, CaCl 2 is hardly detected from dust particles. However, the generation of CaCl 2 becomes detectable around the Japan Islands, where the concentrations of HCl are much higher than those of HNO 3 (½HNO 3 ∕ HCl < ∼0.3). We suggest that elevated concentrations of HCl in the remote marine boundary layer are sufficient to modify Ca-rich particles in dust storms and can play a more important role in forming a deliquescent layer on the particle surfaces as they are transported toward remote ocean regions.heterogeneous reactions | marine atmosphere

No abstract