Granulometry | |
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Basic concepts | |
Particle size, Grain size, Size distribution, Morphology | |
Methods and techniques | |
Mesh scale, Optical granulometry, Sieve analysis, Soil gradation | |
Related concepts | |
Granulation, Granular material, Mineral dust, Pattern recognition, Dynamic light scattering | |
Mineral dust is atmospheric aerosol originated from the suspension of minerals constituting the soil, composed of various oxides and carbonates. Human activities lead to 30% of the airborne dust (particulates) load in the atmosphere. The Sahara Desert is the major source of mineral dust, which subsequently spreads across the Mediterranean (where it is the origin of rain dust) and Caribbean seas into northern South America, Central America, and eastern North America, and Europe. Additionally, it plays a significant role in the nutrient inflow to the Amazon rainforest. [1] The Gobi Desert is another source of dust in the atmosphere, which affects eastern Asia and western North America.
Mineral dust 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 at 1000-5000 million tons per year, [2] 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 and land use changes. [3]
Large dust concentrations may cause problems to people having respiratory problems. Another effect of dust clouds is more colorful sunsets.
The Sahara is the major source on Earth of mineral dust (60-200 million tons per year).[ citation needed ] Saharan dust can be lifted by convection 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 hurricanes.
There is a large variability in the dust transport across the Atlantic into the Caribbean and Florida 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 winds, very large concentrations of mineral dust can be found in the tropical Atlantic, reaching the Caribbean; moreover episodic transport to the Mediterranean region. [4] 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 and other aquatic organisms. Saharan dust carries the fungus Aspergillus sydowii and others. [5] Aspergillus borne by Saharan dust 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. [6] Dust events have been linked to a decline in the health of coral reefs across the Caribbean and Florida, primarily since the 1970s. [7]
According to a NASA article, [8] NASA satellites have shown that "the chilling effect of dust was responsible for one-third of the drop in North Atlantic sea surface temperatures 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.
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. [9] 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[ citation needed ] 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.
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, [10] [11] visibility, [12] [13] lake productivity, [14] and the rate of snowmelt in the Rocky Mountains. [15] Dust deposition has increased dramatically since the early 1800s compared to the natural background [16] [17] [18] due to the intensification of human activities. [19]
Arid and semi-arid regions are naturally prone to dust emissions. [20] 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, [21] to atmospheric burden, [22] to deposition. [23] However, studies based on paleo records of dust deposition (e.g. using lake sediment) that specifically looked at megadroughts show both increases [18] and no change [17] [24] 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. [24] 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.
Desertification is a type of land degradation in drylands in which biological productivity is lost due to natural processes or induced by human activities whereby fertile areas become arid. It is the spread of arid areas caused by a variety of factors, such as overexploitation of soil as a result of human activity and the effects of climate change. Geographic areas most affected include the Sahel region in Africa, the Gobi Desert and Mongolia in Asia as well as parts of South America. Drylands occupy approximately 40–41% of Earth's land area and are home to more than 2 billion people.
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 by saltation and suspension, a process that moves soil from one place and deposits it in another.
The sulfate or sulphate ion is a polyatomic anion with the empirical formula SO2−4. Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many are prepared from that acid.
Global dimming was the name given to a decline in the amount of sunlight reaching the Earth's surface, a measure also known as global direct solar irradiance. It was observed soon after the first systematic measurements of solar irradiance began in the 1950s, and continued until 1980s, with an observed reduction of 4–5% per decade, even though solar activity did not vary more than the usual at the time. Instead, global dimming had been attributed to an increase in atmospheric particulate matter, predominantly sulfate aerosols, as the result of rapidly growing air pollution due to post-war industrialization. After 1980s, global dimming started to reverse, alongside reductions in particulate emissions, in what has been described as global brightening, although this reversal is only considered "partial" for now. This reversal has also been globally uneven, as some of the brightening over the developed countries in the 1980s and 1990s had been counteracted by the increased dimming from the industrialization of the developing countries and the expansion of the global shipping industry, although they have also been making rapid progress in cleaning up air pollution in the recent years.
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 can affect the radiative properties of clouds and the overall atmosphere. Water requires a non-gaseous surface to make the transition from a vapour to a liquid; this process is called condensation.
Aeroplankton are tiny lifeforms that float and drift in the air, carried by wind. Most of the living things that make up aeroplankton are very small to microscopic in size, and many can be difficult to identify because of their tiny size. Scientists collect them for study in traps and sweep nets from aircraft, kites or balloons. The study of the dispersion of these particles is called aerobiology.
The Sahel region of Africa has long experienced a series of historic droughts, dating back to at least the 17th century. The Sahel region is a climate zone sandwiched between the Sudanian Savanna to the south and the Sahara desert to the north, across West and Central Africa. While the frequency of drought in the region is thought to have increased from the end of the 19th century, three long droughts have had dramatic environmental and societal effects upon the Sahel nations. Famine followed severe droughts in the 1910s, the 1940s, and the 1960s, 1970s and 1980s, although a partial recovery occurred from 1975-80. The most recent drought occurred in 2012.
Sea spray are aerosol particles formed from the ocean, mostly by ejection into Earth's atmosphere by bursting bubbles at the air-sea interface. Sea spray contains both organic matter and inorganic salts that form sea salt aerosol (SSA). SSA has the ability to form cloud condensation nuclei (CCN) and remove anthropogenic aerosol pollutants from the atmosphere. Coarse sea spray has also been found to inhibit the development of lightning in storm clouds.
The Saharan Air Layer (SAL) is an extremely hot, dry and sometimes dust-laden layer of the atmosphere that often overlies the cooler, more-humid surface air of the Atlantic Ocean. It carries upwards of 60 million tonnes of dust annually over the ocean and the Americas. This annual phenomenon sometimes cools the ocean and suppresses Atlantic tropical cyclogenesis.
The Bodélé Depression, located at the southern edge of the Sahara Desert in north central Africa, is the lowest point in Chad. It is 500 km long, 150 km wide and around 160 m deep. Its bottom lies about 155 meters above sea level. The dry endorheic basin is a major source of fertile dust essential for the Amazon rainforest.
Coniology or koniology is the study of atmospheric dust and its effects. Samples of dust are often collected by a device called a coniometer. Coniology refers to the observation and contemplation of dust in an atmosphere, but the study of dust may also be applied to dust in space, therefore connecting it to a variety of atmospheric and extraterrestrial topics.
The surface color of the planet Mars appears reddish from a distance because of rusty atmospheric dust. From close up, it looks more of a butterscotch, and other common surface colors include golden, brown, tan, and greenish, depending on minerals.
Iberulites are a particular type of microspherulites that develop in the atmosphere (troposphere), finally falling to the earth's surface. The name comes from the Iberian Peninsula where they were discovered.
Stratospheric aerosol injection is a proposed method of solar geoengineering to reduce global warming. This would introduce aerosols into the stratosphere to create a cooling effect via global dimming and increased albedo, which occurs naturally from volcanic winter. It appears that stratospheric aerosol injection, at a moderate intensity, could counter most changes to temperature and precipitation, take effect rapidly, have low direct implementation costs, and be reversible in its direct climatic effects. The Intergovernmental Panel on Climate Change concludes that it "is the most-researched [solar geoengineering] method, with high agreement that it could limit warming to below 1.5 °C (2.7 °F)." However, like other solar geoengineering approaches, stratospheric aerosol injection would do so imperfectly and other effects are possible, particularly if used in a suboptimal manner.
Rain dust or snow dust, traditionally known as muddy rain, red rain, or coloured rain, is a variety of rain which contains enough mineral dust, from soils, for the dust to be visible without using a microscope.
Particulates or atmospheric particulate matter are microscopic particles of solid or liquid matter suspended in the air. The term aerosol commonly refers to the particulate/air mixture, as opposed to the particulate matter alone. Sources of particulate matter can be natural or anthropogenic. They have impacts on climate and precipitation that adversely affect human health, in ways additional to direct inhalation.
The African humid period is a climate period in Africa during the late Pleistocene and Holocene geologic epochs, when northern Africa was wetter than today. The covering of much of the Sahara desert by grasses, trees and lakes was caused by changes in the Earth's axial tilt; changes in vegetation and dust in the Sahara which strengthened the African monsoon; and increased greenhouse gases. During the preceding Last Glacial Maximum, the Sahara contained extensive dune fields and was mostly uninhabited. It was much larger than today, and its lakes and rivers such as Lake Victoria and the White Nile were either dry or at low levels. The humid period began about 14,600–14,500 years ago at the end of Heinrich event 1, simultaneously to the Bølling–Allerød warming. Rivers and lakes such as Lake Chad formed or expanded, glaciers grew on Mount Kilimanjaro and the Sahara retreated. Two major dry fluctuations occurred; during the Younger Dryas and the short 8.2 kiloyear event. The African humid period ended 6,000–5,000 years ago during the Piora Oscillation cold period. While some evidence points to an end 5,500 years ago, in the Sahel, Arabia and East Africa, the end of the period appears to have taken place in several steps, such as the 4.2-kiloyear event.
The North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) was a five-year scientific research program that investigated aspects of phytoplankton dynamics in ocean ecosystems, and how such dynamics influence atmospheric aerosols, clouds, and climate. The study focused on the sub-arctic region of the North Atlantic Ocean, which is the site of one of Earth's largest recurring phytoplankton blooms. The long history of research in this location, as well as relative ease of accessibility, made the North Atlantic an ideal location to test prevailing scientific hypotheses in an effort to better understand the role of phytoplankton aerosol emissions on Earth's energy budget.
Saharan dust is an aeolian mineral dust from the Sahara desert, the largest hot desert in the world. The desert spans just over 9 million square kilometers, from the Atlantic Ocean to the Red Sea, from the Mediterranean sea to the Niger River valley and the Sudan region in the south.
Georgiy L. Stenchikov is an applied mathematician and climate scientist focusing on studies of physical processes that govern the Earth's climate. He is a professor in the Department of Earth Science and Engineering at the King Abdullah University of Science and Technology in Saudi Arabia.