Aerosol
Encyclopedia
Technically, an aerosol is a suspension
of fine solid
particles or liquid
droplets in a gas
. Examples are clouds, and air pollution
such as smog and smoke. In general conversation, aerosol usually refers to an aerosol spray
can or the output of such a can. The word aerosol derives from the fact that matter "floating" in air is a suspension (a mixture in which solid or liquid or combined solid–liquid particles are suspended in a fluid
). To differentiate suspension
s from true solution
s, the term sol
evolved—originally meant to cover dispersions
of tiny (sub-microscopic) particles in a liquid. With studies of dispersions in air, the term aerosol evolved and now embraces both liquid droplets, solid particles, and combinations of these.
The Earth atmosphere contains aerosols of various types and concentrations, including quantities of:
By far the most common aerosols in the atmosphere are clouds, which normally consist of suspensions of water
droplets or ice particles of greater or lesser density.
Aerosols can be found in urban Ecosystem
s in various forms, for example:
aerosols from fossil fuel
combustion, exert a cooling influence on the climate which partly counteracts the warming induced by greenhouse gases such as carbon dioxide. This effect is accounted for in many climate models. Recent research suggests that aerosol diffusion of light may have increased the carbon sink in the Earth's ecosystem.
Recent studies of the Sahel drought
and major increases since 1967 in rainfall over the Northern Territory
, Kimberley, Pilbara and around the Nullarbor Plain
have led some scientists to conclude that the aerosol haze over South
and East Asia
has been steadily shifting tropical rainfall in both hemispheres southward. The latest studies of severe rainfall declines over southern Australia
since 1997 have led climatologists there to consider the possibility that these Asian aerosols have shifted not only tropical but also midlatitude systems southward.
Oxides of nitrogen
(NOx) in the atmosphere are a form of pollution which can give rise to smog
and act as a greenhouse gas
. Their persistence in the atmosphere is affected by aerosol droplets of water. In 1964 long chain fatty acids, either naturally produced from marine organisms dispersed into the atmosphere by wave action or man-made, were found to coat these droplets. In 2006 there was a study of the effect of the LCFA on the persistence of NOx, but the long term implications, although thought to be significant, have yet to be determined.
Currently, the net effect of the most common short-lived aerosol pollutants on climate change
is small, as the radiative forcing of different species nearly cancels. Reduced emissions of sulphur dioxide, leading to lower concentrations of cooling sulphates, combined with projected increases in emission of black carbon
aerosols (assuming no worldwide shift to a green economy
) will lead to a net warming effect from these species. In the long run, regional effects resulting from emissions patterns are projected to average out, with this warming following the geographic distribution of warming from well-mixed greenhouse gases.
particles could coat with dust particles and sulfate could envelope particles of soot, but the assumptions made is that the particles remain separate.Mixed aerosols have different characteristics compared to particles that are separate.
Suspension (chemistry)
In chemistry, a suspension is a heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometer. The internal phase is dispersed throughout the external phase through mechanical agitation, with the use of certain...
of fine solid
Solid
Solid is one of the three classical states of matter . It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a...
particles or liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
droplets in a gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
. Examples are clouds, and air pollution
Air pollution
Air pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or cause damage to the natural environment or built environment, into the atmosphere....
such as smog and smoke. In general conversation, aerosol usually refers to an aerosol spray
Aerosol spray
Aerosol spray is a type of dispensing system which creates an aerosol mist of liquid particles. This is used with a can or bottle that contains a liquid under pressure. When the container's valve is opened, the liquid is forced out of a small hole and emerges as an aerosol or mist...
can or the output of such a can. The word aerosol derives from the fact that matter "floating" in air is a suspension (a mixture in which solid or liquid or combined solid–liquid particles are suspended in a fluid
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....
). To differentiate suspension
Suspension (chemistry)
In chemistry, a suspension is a heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometer. The internal phase is dispersed throughout the external phase through mechanical agitation, with the use of certain...
s from true solution
Solution
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...
s, the term sol
Sol (colloid)
A sol is a colloidal suspension of very small solid particles in a continuous liquid medium. They are quite stable and show the Tyndall effect. Examples include blood, pigmented ink, and paint....
evolved—originally meant to cover dispersions
Dispersion (chemistry)
A dispersion is a system in which particles are dispersed in a continuous phase of a different composition . See also emulsion. A dispersion is classified in a number of different ways, including how large the particles are in relation to the particles of the continuous phase, whether or not...
of tiny (sub-microscopic) particles in a liquid. With studies of dispersions in air, the term aerosol evolved and now embraces both liquid droplets, solid particles, and combinations of these.
The Earth atmosphere contains aerosols of various types and concentrations, including quantities of:
- natural inorganicInorganic chemistryInorganic chemistry is the branch of chemistry concerned with the properties and behavior of inorganic compounds. This field covers all chemical compounds except the myriad organic compounds , which are the subjects of organic chemistry...
materials: dust, smoke, sea salt, water droplets. - natural organicOrganic chemistryOrganic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, composition, reactions, and preparation of carbon-based compounds, hydrocarbons, and their derivatives...
materials: pollenPollenPollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...
, sporeSporeIn biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s, bacteriaBacteriaBacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals... - anthropogenic products of combustion such as: smoke, ashesFly ashFly ash is one of the residues generated in combustion, and comprises the fine particles that rise with the flue gases. Ash which does not rise is termed bottom ash. In an industrial context, fly ash usually refers to ash produced during combustion of coal...
oder dusts
By far the most common aerosols in the atmosphere are clouds, which normally consist of suspensions of water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
droplets or ice particles of greater or lesser density.
Aerosols can be found in urban Ecosystem
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
s in various forms, for example:
- Dust,
- Cigarette smoke,
- Mist from aerosol sprayAerosol sprayAerosol spray is a type of dispensing system which creates an aerosol mist of liquid particles. This is used with a can or bottle that contains a liquid under pressure. When the container's valve is opened, the liquid is forced out of a small hole and emerges as an aerosol or mist...
cans, - Soot or fumes in car exhaust.
Effect on climate
Some anthropogenic aerosols, particularly sulfateSulfate
In inorganic chemistry, a sulfate is a salt of sulfuric acid.-Chemical properties:...
aerosols from fossil fuel
Fossil fuel
Fossil fuels are fuels formed by natural processes such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years...
combustion, exert a cooling influence on the climate which partly counteracts the warming induced by greenhouse gases such as carbon dioxide. This effect is accounted for in many climate models. Recent research suggests that aerosol diffusion of light may have increased the carbon sink in the Earth's ecosystem.
Recent studies of the Sahel drought
Sahel drought
[[File:Greening Sahel 1982-1999.jpg|thumb|300px|Recent "Greening" of the Sahel: The results of trend analyses of time series over the Sahel region of seasonally integrated NDVI using NOAA AVHRR NDVI-data from 1982 to 1999...
and major increases since 1967 in rainfall over the Northern Territory
Northern Territory
The Northern Territory is a federal territory of Australia, occupying much of the centre of the mainland continent, as well as the central northern regions...
, Kimberley, Pilbara and around the Nullarbor Plain
Nullarbor Plain
The Nullarbor Plain is part of the area of flat, almost treeless, arid or semi-arid country of southern Australia, located on the Great Australian Bight coast with the Great Victoria Desert to its north. It is the world's largest single piece of limestone, and occupies an area of about...
have led some scientists to conclude that the aerosol haze over South
South Asia
South Asia, also known as Southern Asia, is the southern region of the Asian continent, which comprises the sub-Himalayan countries and, for some authorities , also includes the adjoining countries to the west and the east...
and East Asia
East Asia
East Asia or Eastern Asia is a subregion of Asia that can be defined in either geographical or cultural terms...
has been steadily shifting tropical rainfall in both hemispheres southward. The latest studies of severe rainfall declines over southern Australia
Climate change in Australia
Climate change has become a major issue in Australia due to drastic climate events since the turn of the 21st century that have focused government and public attention. Rainfall in Australia has increased slightly over the past century, although there is little or no trend in rainfall in northeast...
since 1997 have led climatologists there to consider the possibility that these Asian aerosols have shifted not only tropical but also midlatitude systems southward.
Oxides of nitrogen
Nitrogen oxide
Nitrogen oxide can refer to a binary compound of oxygen and nitrogen, or a mixture of such compounds:* Nitric oxide, also known as nitrogen monoxide, , nitrogen oxide* Nitrogen dioxide , nitrogen oxide...
(NOx) in the atmosphere are a form of pollution which can give rise to smog
Smog
Smog is a type of air pollution; the word "smog" is a portmanteau of smoke and fog. Modern smog is a type of air pollution derived from vehicular emission from internal combustion engines and industrial fumes that react in the atmosphere with sunlight to form secondary pollutants that also combine...
and act as a greenhouse gas
Greenhouse gas
A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...
. Their persistence in the atmosphere is affected by aerosol droplets of water. In 1964 long chain fatty acids, either naturally produced from marine organisms dispersed into the atmosphere by wave action or man-made, were found to coat these droplets. In 2006 there was a study of the effect of the LCFA on the persistence of NOx, but the long term implications, although thought to be significant, have yet to be determined.
Currently, the net effect of the most common short-lived aerosol pollutants on climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...
is small, as the radiative forcing of different species nearly cancels. Reduced emissions of sulphur dioxide, leading to lower concentrations of cooling sulphates, combined with projected increases in emission of black carbon
Black carbon
In Climatology, black carbon or BC is a climate forcing agent formed through the incomplete combustion of fossil fuels, biofuel, and biomass, and is emitted in both anthropogenic and naturally occurring soot. It consists of pure carbon in several linked forms...
aerosols (assuming no worldwide shift to a green economy
Green economy
A green economy is one that results in improved human well-being and social equity, while significantly reducing environmental risks and ecological scarcities - United Nations Environment Programme...
) will lead to a net warming effect from these species. In the long run, regional effects resulting from emissions patterns are projected to average out, with this warming following the geographic distribution of warming from well-mixed greenhouse gases.
Effect on India's Climate
The effects of aerosol on climate was pronounced over central and northern India.It has led to a reduction in the monsoon rainfall over India in the past 50 years and above.This was published online by the journal Science.It is based on a study done by Massimo Bollasina of Princeton university in the U.S., along with Yi Ming and V.Ramaswamy of the Geological Fluid dynamics Laboratory at Princeton,used a state-of-the-art global climate model to simulate what was happening in the Indian ocean with and without human-generated aerosols..However Indian scientists have expressed reservations and claim that the model used in this study has certain wrong assumptions.They support their claim by mentioning that the sootSoot
Soot is a general term that refers to impure carbon particles resulting from the incomplete combustion of a hydrocarbon. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolyzed fuel particles such as cenospheres,...
particles could coat with dust particles and sulfate could envelope particles of soot, but the assumptions made is that the particles remain separate.Mixed aerosols have different characteristics compared to particles that are separate.
See also
- Aerosol scienceAerosol scienceAerosol science is the rapidly expanding field of science which investigates the physical, chemical, and biological properties of aerosolized materials , which behave in ways that make them unique from even other forms of similar materials...
- NebulizerNebulizerIn medicine, a nebulizer is a device used to administer medication in the form of a mist inhaled into the lungs....
- AerogelAerogelAerogel is a synthetic porous material derived from a gel, in which the liquid component of the gel has been replaced with a gas. The result is a solid with extremely low density and thermal conductivity...
- Charged particleCharged particleIn physics, a charged particle is a particle with an electric charge. It may be either a subatomic particle or an ion. A collection of charged particles, or even a gas containing a proportion of charged particles, is called a plasma, which is called the fourth state of matter because its...
- Aerosol sprayAerosol sprayAerosol spray is a type of dispensing system which creates an aerosol mist of liquid particles. This is used with a can or bottle that contains a liquid under pressure. When the container's valve is opened, the liquid is forced out of a small hole and emerges as an aerosol or mist...
, the spraying device - BioaerosolBioaerosolA bioaerosol is a suspension of airborne particles that contain living organisms or were released from living organisms. These particles are very small and range in size from less than one micrometer to one hundred micrometers . Bioaerosols react to air currents and move quickly or slowly...
- Global dimmingGlobal dimmingGlobal dimming is the gradual reduction in the amount of global direct irradiance at the Earth's surface that was observed for several decades after the start of systematic measurements in the 1950s. The effect varies by location, but worldwide it has been estimated to be of the order of a 4%...
- Particulate, mixed-phase state of matter
- PollutionPollutionPollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...
- Stratospheric Aerosol and Gas ExperimentStratospheric Aerosol and Gas ExperimentThe Stratospheric Aerosol and Gas Experiment is a series of remote sensing satellite instruments used to study the chemical composition of earth's atmosphere. Specifically, SAGE has been used to study the Earth's ozone layer and aerosols at the troposhere through the stratosphere...
(SAGE)
External links
- American Association for Aerosol Research
- An on-line aerosol calculator
- Climate change and aerosols. Dr Jim Haywood of the Hadley Centre explains how aerosols affect the world's climate.
- NASA GISS: Science Briefs: Particles Multi-Task to Change Climate. Dr Dorothy Koch of the Goddard Institute for Space StudiesGoddard Institute for Space StudiesThe NASA Goddard Institute for Space Studies , at Columbia University in New York City, is a component laboratory of NASA's Goddard Space Flight Center Earth-Sun Exploration Division and a unit of The Earth Institute at Columbia University...
explains how aerosols can act to both warm and cool the climate. - CAPCO (www.aerosolproducts.org) is a nonprofit organization dedicated to providing accurate information about aerosol products
- The Aerosol Products Division (www.aboutaerosols.com) of the Consumer Specialty Products Association also gives facts and relevant information about aerosol products