A review of methods for long term in situ characterization of aerosol dust

Desert dust emitted and transported to distant regions influence on the climate, biogeochemistry and air quality of our planet. Long term (multi-decadal) measurements of aerosol dust with in situ characterization techniques are crucial for understanding the interactions of dust with the Earth system. We reviewed the programs which have been performing such long term dust monitoring. First long term observations started in the North Atlantic during the 1960s. Although dust programs rapidly expanded during the 1980s and 1990s, mostly across the Pacific and Atlantic oceans, only a few sites that have been active in the last 20–30 years continue operative nowadays. We reviewed the techniques that are available for in situ aerosol dust characterization. Techniques for long term measurement of mass concentration, size distribution, bulk composition, optical properties are nowadays available. Other techniques that are not regularly used in (or designed for) long term programs are also described; these may be incorporated into long term programs in specific periods (e.g. dust season on a year-to-year basis). Their implementation in long term programs allow us to study potential changes in the sources of some key minerals linked to changes in the strength and location of dust sources, and/or the mixing state of dust with pollutants related to the evolution of anthropogenic emissions. Given that some of these methods are not specifically designed for dust, some considerations should be addressed when the techniques are used for aerosol dust measurements. Accuracy, sources of errors, corrections and features of dust measurements are reviewed.