Mineral dust is atmospheric aerosol originated from the suspension of

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...

s constituting the

soil Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by re ...

, composed of various

oxide An oxide () is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of −2) of oxygen, an O2− ion with oxygen in the oxidation st ...

s and

carbonate A carbonate is a salt of carbonic acid, (), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word "carbonate" may also refer to a carbonate ester, an organic compound containing the carbonate group ...

s. Human activities lead to 25% of the airborne dust (

particulates Particulate matter (PM) or particulates are microscopic particles of solid or liquid matter suspension (chemistry), suspended in the atmosphere of Earth, air. An ''aerosol'' is a mixture of particulates and air, as opposed to the particulate ...

) load in the

atmosphere An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

. The

Sahara Desert The Sahara (, ) is a desert spanning across North Africa. With an area of , it is the largest hot desert in the world and the list of deserts by area, third-largest desert overall, smaller only than the deserts of Antarctica and the northern Ar ...

is the major source of mineral

dust Dust is made of particle size, fine particles of solid matter. On Earth, it generally consists of particles in the atmosphere that come from various sources such as soil lifted by wind (an aeolian processes, aeolian process), Types of volcan ...

, which subsequently spreads across the

Mediterranean The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern ...

(where it is the origin of rain dust) and

Caribbean The Caribbean ( , ; ; ; ) is a region in the middle of the Americas centered around the Caribbean Sea in the Atlantic Ocean, North Atlantic Ocean, mostly overlapping with the West Indies. Bordered by North America to the north, Central America ...

seas into northern

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

Central America Central America is a subregion of North America. Its political boundaries are defined as bordering Mexico to the north, Colombia to the southeast, the Caribbean to the east, and the Pacific Ocean to the southwest. Central America is usually ...

, and eastern

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

, and

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

. Additionally, it plays a significant role in the nutrient inflow to the

Amazon rainforest The Amazon rainforest, also called the Amazon jungle or Amazonia, is a Tropical and subtropical moist broadleaf forests, moist broadleaf tropical rainforest in the Amazon biome that covers most of the Amazon basin of South America. This basin ...

. The

Gobi Desert The Gobi Desert (, , ; ) is a large, cold desert and grassland region in North China and southern Mongolia. It is the sixth-largest desert in the world. The name of the desert comes from the Mongolian word ''gobi'', used to refer to all of th ...

is another source of dust in the atmosphere, which affects eastern

Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

and western North America.

Characteristics

Mineral dust is mainly constituted of the

s (SiO₂, Al₂O₃, FeO, Fe₂O₃, CaO, and others) and

s (CaCO₃, MgCO₃) that constitute the

Earth's crust Earth's crust is its thick outer shell of rock, referring to less than one percent of the planet's radius and volume. It is the top component of the lithosphere, a solidified division of Earth's layers that includes the crust and the upper ...

. The composition of mineral dust, usually named in atmospheric sciences as mineralogy composition, is relevant for different physical and chemical processes in the atmosphere, for example, oxides with iron have an effect in the optical properties with impact in climate, while minor components can modify the role in the atmosphere of mineral dust as

cloud condensation nuclei Cloud condensation nuclei (CCNs), also known as cloud seeds, are small particles typically 0.2 μm, or one hundredth the size of a cloud droplet. CCNs are a unique subset of aerosols in the atmosphere on which water vapour condenses. This c ...

. Global mineral dust emissions are estimated at 1000-5000 million 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 a quarter of mineral dust emissions could be ascribed to human activities through

desertification Desertification is a type of gradual land degradation of Soil fertility, fertile land into arid desert due to a combination of natural processes and human activities. The immediate cause of desertification is the loss of most vegetation. This i ...

and land use changes. Recent studies highlight that the fraction of large particles (called coarse dust) may be higher than previously thought and total emissions would be therefore also higher. Large dust concentrations may cause problems to people having respiratory problems. Another effect of dust clouds is more colorful

sunset Sunset (or sundown) is the disappearance of the Sun at the end of the Sun path, below the horizon of the Earth (or any other astronomical object in the Solar System) due to its Earth's rotation, rotation. As viewed from everywhere on Earth, it ...

Saharan dust

The Sahara is the major source on Earth of mineral dust (60-200 million tons per year). Saharan dust can be lifted by

convection Convection is single or Multiphase flow, multiphase fluid flow that occurs Spontaneous process, spontaneously through the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoy ...

over hot desert 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 extremely 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

hurricane A tropical cyclone is a rapidly rotating storm system with a low-pressure area, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its ...

s. There is a large variability in the dust transport across the

Atlantic The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for se ...

into the

and

Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...

from year to year. In some years African dust is observed along much of the East Coast of the United States and is visible in the sky. Due to the

trade wind The trade winds or easterlies are permanent east-to-west prevailing winds that flow in the Earth's equatorial region. The trade winds blow mainly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere, ...

s, very large concentrations of mineral dust can be found in the tropical Atlantic, reaching the Caribbean; moreover episodic transport to the

region. Saharan plumes can form iberulites (a particular tropospheric aggregation of aerosols) when these plumes travel through North Africa and the eastern North Atlantic Ocean, and often reach the circum-Mediterranean areas of Western Europe. In the Mediterranean region, Saharan dust is important as it represents the major source of nutrients for

phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater Aquatic ecosystem, ecosystems. The name comes from the Greek language, Greek words (), meaning 'plant', and (), mea ...

and other aquatic organisms. Saharan dust carries the fungus '' Aspergillus sydowii'' and others. Aspergillus borne by Saharan dust falls into the

Caribbean Sea The Caribbean Sea is a sea of the Atlantic Ocean, North Atlantic Ocean in the tropics of the Western Hemisphere, located south of the Gulf of Mexico and southwest of the Sargasso Sea. It is bounded by the Greater Antilles to the north from Cuba ...

and possibly infects

coral reefs A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups. ...

with Sea Fan disease (

aspergillosis Aspergillosis is a fungal infection of usually the lungs, caused by the genus ''Aspergillus'', a common mold that is breathed in frequently from the air, but does not usually affect most people. It generally occurs in people with lung diseases su ...

). It also has been linked to increased incidence of pediatric

asthma Asthma is a common long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wh ...

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 reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in group ...

s across the

and

, primarily since the 1970s.

Effect on hurricane frequency

According to a

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

article, NASA satellites have shown that "the chilling effect of dust was responsible for one-third of the drop in North Atlantic

sea surface temperature Sea surface temperature (or ocean surface temperature) is the ocean temperature, temperature of ocean water close to the surface. The exact meaning of ''surface'' varies in the literature and in practice. It is usually between and below the sea ...

s between June 2005 and 2006, possibly contributing to the difference in hurricane activity between the two seasons." There were only 5 hurricanes in 2006 compared with 15 in 2005. It is known that one of the major factors that create hurricanes is warm water temperatures on the surface of the ocean. Evidence shows that dust from the Sahara desert caused surface temperatures to be cooler in 2006 than in 2005.

Asian dust

In Eastern Asia, mineral dust events that originate in the Gobi Desert (Southern Mongolia and Northern China) during springtime give 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 enriches 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 Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...

, possibly incorporated in the air mass as it passes over industrialized regions in Asia. Although

dust storms A dust storm, also called a sandstorm, is a meteorological phenomenon common in arid and semi-arid regions. Dust storms arise when a gust front or other strong wind blows loose sand and dirt from a dry surface. Fine particles are transported ...

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

North American dust

Mineral dust originates from several sources on the North American continent including the Southwest, the Great Plains, and Alaska. In the Southwest, dust impacts human health, visibility, lake productivity, and the rate of snowmelt in the Rocky Mountains. Dust deposition has increased dramatically since the early 1800s compared to the natural background due to the intensification of human activities.

Relationship to drought

Arid and semi-arid regions are naturally prone to dust emissions. Soil moisture is an important variable controlling dust emissions, along with vegetation cover, wind speed and soil type. Several studies based on modern observations show positive relationships (i.e. increasing drought increases dust) between dust and drought conditions in each dust cycle phase, from emissions, to atmospheric burden, to deposition. However, studies based on paleo records of dust deposition (e.g. using lake sediment) that specifically looked at megadroughts show both increases and no change in dust deposition. The study by Routson showed an increase in deposition during megadroughts but used a measure of dust concentration rather than accumulation that is affected by the rate of sedimentation. The Routson study instead used dust accumulation rates and found no difference between dust deposition during drought years and megadroughts and deposition during normal hydroclimate conditions. Instead, they found that dust deposition is more likely controlled by transport mechanisms and sediment supply than by hydroclimate. Similarly, Arcusa found no evidence for higher dust deposition during drought on multi-decadal and centennial scales. They also found that sediment supply played a key role as evidenced from a 60% increase in deposition in the 1800s due to accelerating land disturbance.

References

* Kubilay and Saydam, "Trace elements in atmospheric particulates over the Eastern Mediterranean: concentration, sources, and temporal variability", ''Atmospheric Environment'' 29, 2289-2300 (1995). * Morales, "The airborne transport of Saharan dust: a review", ''Climate Change'' 9, 219-241 (1986). * Loyë-Pilot ''et al.'', "Influence of Saharan dust on the rain acidity and atmospheric input to the Mediterranean", ''Nature'' 321, 427-428 (1986). * Sokolik and Toon, "Direct radiative forcing by anthropogenic airborne mineral aerosols", ''Nature'' 381, 681-683 (1996). * Tegen and Fung, "Contribution to the atmospheric mineral aerosol load from land surface modification", ''Journal of Geophysical Research'' 100, 18707-18726 (1995).

External links

The Dust Hypothesis for Caribbean Coral Bleaching
as reported by the

United States Geological Survey The United States Geological Survey (USGS), founded as the Geological Survey, is an agency of the U.S. Department of the Interior whose work spans the disciplines of biology, geography, geology, and hydrology. The agency was founded on Mar ...

Saharan dust in America
{{Webarchive, url=https://web.archive.org/web/20070929102919/http://www.exn.ca/Stories/1999/07/13/53.asp , date=2007-09-29
High quality video of dust from Sahara to Amazon
Atmosphere Dust