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Mineral dust is a term used to indicate atmospheric aerosols originated from the suspension of minerals constituting the soil, being comprised of various oxides and carbonates. Human activities lead to 30% of the dust load in the atmosphere. The Sahara is the major source of mineral dust, which subsequently spreads across the Mediterranean and Caribbean seas into northern South America, Central America, North America, and Europe. The Gobi Desert is another source of dust in the atmosphere, which affects eastern Asia and western North America.
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It is mainly constituted of the oxides (SiO2, Al2O3, FeO, Fe2O3, CaO, and others) and carbonates (CaCO3, MgCO3) that constitute the Earth's crust. Global mineral dust emissions are estimated 100-500 millions of tons per year, of which the largest part is attributed to deserts. Although this aerosol class is usually considered of natural origin, it is estimated that about 30% of the mineral dust load in the atmosphere could be ascribed to human activities through desertification and land misuse. Large dust concentrations may cause problems to people having respiratory problems, forcing them to stay indoors while dust aerosols are in the area. Another notable effect of dust clouds is prettier sunsets, thanks to the increased number of particles in the sky, which the Sun may reflect off of.
The Sahara is the major source on Earth of mineral dust (60-200 millions of tons per year). Saharan dust can be lifted by convection over hot desertic areas, and can thus reach very high altitudes; from there it can be transported worldwide by winds, covering distances of thousands of kilometers. The dust combined with the hot dry air of the Sahara Desert often forms an atmospheric layer called the Saharan Air Layer which has significant effects on tropical weather, especially as it interferes with the development of hurricanes. There is a large variability in the dust transport across the Atlantic into the Caribbean and Florida from year to year. Due to the trade winds, very large concentrations of mineral dust can be found in the tropical Atlantic, reaching the Caribbean; moreover episodic transport to the Mediterranean region as well as Northern Europe is observed. In the Mediterranean region, Saharan dust is important as it represents the major source of nutrients for phytoplancton and other aquatic organisms. Saharan dust carries the fungus Aspergillus sydowii which falls into the Caribbean Sea and possibly infects coral reefs with Sea Fan disease (aspergillosis). It also has been linked to increased incidence of pediatric asthma attacks in the Caribbean. Since 1970, dust outbreaks have worsened due to periods of drought in Africa. Dust events have been linked to a decline in the health of coral reefs across the Caribbean and Florida, primarily since the 1970s.
In Eastern Asia, mineral dust events originated in springtime in the Gobi Desert (Southern Mongolia and Northern China) gives rise to the phenomenon called Asian dust. The aerosols are carried eastward by prevailing winds, and pass over China, Korea, and Japan. Sometimes, significant concentrations of dust can be carried as far as the Western United States. Areas affected by Asian dust experience decreased visibility and health problems, such as sore throat and respiratory difficulties. The effects of Asian dust, however, are not strictly negative, as it is thought that its deposition enrichs the soil with important trace minerals. An American study analyzing the composition of Asian dust events reaching Colorado associates them to the presence of carbon monoxide, possibly incorporated in the air mass as it passes over industrialized regions in Asia. Although dust storms in the Gobi desert have occurred from time to time throughout history, they became a pronounced problem in the second half of the 20th century due to intensified agricultural pressure and desertification.
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|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Mineral_dust". A list of authors is available in Wikipedia.|