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Particulate matter suspended in air mainly consists of a complex, multiphase system. Its nature is largely mineral at a global scale, and it has a significant physicochemical impact on the Earth’s atmosphere and on biogeochemical cycles. These mineral phases come mainly from windblown soil processes, mostly from great deserts. Despite their importance, the behaviour of their airborne components in time and space is not well known.

This study found that the rate of mineral deposition over an annual cycle in the south-eastern Iberian Peninsula was 26.03 g m(-2) yr(-1), with maxima in spring and summer. Using powder X-Ray diffraction techniques, this value has been broken down as follows (in g m(-2) yr(-1)): quartz (4.90), dolomite (3.36), calcite (3.28), micas (2.97), smectites (2.10), halite (1.84), kaolinite (1.82), sulphates (1.28), amorphous matter (1.15), feldspars (0.18) and graphite (0.17). Although quartz normally is the major individual component of solid particles in the atmosphere carbonates (calcite + dolomite) can exceed quartz, and phyllosilicates can total as much as carbonates. Clay minerals correlate well with salts (sulphates and halite), and there is an antagonistic relation between sulphates and calcite. Amorphous matter consists of a mixture of metal oxides and organic compounds, among others. Graphite, a net anthropogenic constituent of atmospheric dust, only represents minor quantities.

The behavioural differences of the minerals are due to their different reactivity, based on their intrinsic properties of specific surface area, deliquescence, swelling and water retention capacity, and the presence of metallic and exchangeable cations. Smectites seem to play an essential role in the atmospheric processing of SO2 and in secondary sulphate genesis. (C) 2011 Elsevier Ltd. All rights reserved.