Aerosol pollution over Northern India and Bangladesh - NASA

Cloud condensation nuclei or CCNs (also known as cloud seeds) are small particles (typically 0.0002 mm, or 1/100 th the size of a cloud droplet [1]) about which cloud droplets coalesce. Water requires a non-gaseous surface to make the transition from a vapour to a liquid. In the atmosphere, this surface presents itself as tiny solid or liquid particles called CCNs. When no CCNs are present, water vapour can be supercooled below 0 °C (32 °F) before droplets spontaneously form (this is the basis of the cloud chamber for detecting subatomic particles). In above freezing temperatures the air would have to be supersaturated to around 400% before the droplets could form. The concept of cloud condensation nuclei has led to the idea of cloud seeding, that tries to encourage rainfall by seeding the air with condensation nuclei appropriately Download high resolution version (1100x1450, 311 KB)Aerosol pollution over Northern India and Bangladesh File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Download high resolution version (1100x1450, 311 KB)Aerosol pollution over Northern India and Bangladesh File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... For other uses, see Cloud (disambiguation). ... Look up coalescence in Wiktionary, the free dictionary. ... Vapor (US English) or vapour (British English) is the gaseous state of matter. ... For other uses, see Liquid (disambiguation). ... Boundaries: Phase, Pressure, Temperature Evaporation/Sublimation Whenever a water molecule leaves a surface, it is said to have evaporated. ... The degree Celsius (°C) is a unit of temperature named after the Swedish astronomer Anders Celsius (1701–1744), who first proposed a similar system in 1742. ... Fahrenheit is a temperature scale named after the German physicist Gabriel Fahrenheit (1686–1736), who proposed it in 1724. ... Discovery of the positron in 1932 by Carl D. Anderson in a cloud chamber The cloud chamber, also known as the Wilson chamber, is used for detecting particles of ionizing radiation. ... Cessna 210 with cloud seeding equipment Cloud seeding, a form of weather modification, is the attempt to change the amount or type of precipitation that falls from clouds, by dispersing substances into the air that serve as cloud condensation or ice nuclei. ...

Size, abundance, and composition

A typical raindrop is about 2 mm in diameter, a typical cloud droplet is on the order of 0.02 mm, and a typical cloud condensation nucleus (aerosol) is on the order of 0.0001 mm or 0.1 micrometer or greater in diameter. The number of cloud condensation nuclei in the air can be measured and ranges between around 100 to 1000 per cubic centimetre. The total mass of CCNs injected into the atmosphere has been estimated at 2x10¹² kg over a year's time. Large concentrations of particulates are also responsible for haze in areas with lower humidity. This dry haze also has an effect on climate by either absorbing or reflecting radiation (see albedo). Particulates, alternatively referred to as particulate matter (PM), aerosols or fine particles, are tiny particles of solid or liquid suspended in a gas. ... Haze is an atmospheric phenomenon where dust, smoke and other pollutant particles obscure the normal clarity of the sky. ... Humidity is the amount of water vapor in air. ... Albedo is the ratio of reflected to incident electromagnetic radiation. ...

There are many different types of atmospheric particulates that can act as CCN. The particles may be composed of dust or clay, soot or black carbon from grassland or forest fires, sea salt from ocean wave spray, soot from factory smokestacks or internal combustion engines, sulfate from volcanic activity, phytoplankton or the oxidation of sulfur dioxide and secondary organic matter formed by the oxidation of VOCs. The ability of these different types of particles to form cloud droplets varies according to their size and also their exact composition, as the hygroscopic properties of these different constituents are very different. Sulfate and sea salt, for instance, readily absorb water whereas soot, organic carbon and mineral particles do not. This is made even more complicated by the fact that many of the chemical species may be mixed within the particles (in particular the sulfate and organic carbon). Additionally, while some particles (such as soot and minerals) do not make very good CCN, they do act as very good ice nuclei in colder parts of the atmosphere. Particulates, alternately referred to as Particulate Matter (PM) , aerosols or fine particles are tiny particles of solid or liquid suspended in the air. ... For other uses, see Clay (disambiguation). ... Soot, also called lampblack, Pigment Black 7, carbon black or black carbon, is a dark powdery deposit of unburned fuel residues, usually composed mainly of amorphous carbon, that accumulates in chimneys, automobile mufflers and other surfaces exposed to smoke—especially from the combustion of carbon-rich organic fuels in the... The sulfate anion, SO42− The structure and bonding of the sulfate ion In inorganic chemistry, a sulfate (IUPAC-recommended spelling; also sulphate in British English) is a salt of sulfuric acid. ... This article is about volcanoes in geology. ... Diagrams of some typical phytoplankton Phytoplankton are the autotrophic component of plankton. ... Sulfur dioxide (or Sulphur dioxide) has the chemical formula SO2. ... ... A hygroscopic substance is a substance that absorbs water readily from its surroundings. ... Ice nuclei are particles that act as nuclei for the formation of ice crystals in the atmosphere. ...

The number and type of CCNs can affect the lifetimes and radiative properties of clouds as well as the amount and hence have an influence on climate change [2] [3], but the details of this are still not well understood but are the subject of much research by many groups worldwide. For other uses, see Cloud (disambiguation). ... Variations in CO2, temperature and dust from the Vostok ice core over the last 450,000 years For current global climate change, see Global warming. ...

Phytoplankton bloom in the North Sea and the Skagerrak - NASA

Phytoplankton bloom in the North Sea and the Skagerrak - NASA File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Phytoplankton bloom in the North Sea and the Skagerrak - NASA File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...

Phytoplankton role

Main article: CLAW hypothesis

Sulfate aerosol (SO₄^2- and methanesulfonic acid droplets) act as CCNs. These sulfate aerosols form partly from the dimethyl sulfide (DMS) produced by phytoplankton in the open ocean. Large algal blooms in ocean surface waters occur in a wide range of latitudes and no doubt contribute considerable DMS into the atmosphere to act as nuclei. The idea that an increase in global temperature would also increase phytoplankton activity and therefore CCN numbers was seen as a possible natural phenomenon that would counteract climate change. This is known as the CLAW hypothesis [4] (named after the authors' initials of a 1987 Nature paper) but no conclusive evidence to support this has yet been reported. The CLAW hypothesis proposes a feedback loop that operates between ocean ecosystems and the Earths climate[1]. The hypothesis specifically proposes that particular phytoplankton that produce dimethyl sulfide are responsive to variations in climate forcing, and that these responses lead to a negative feedback loop that acts to stabilise... Dimethyl sulfide causes that distinctive smell from your St. ... Algal blooms can present problems for ecosystems and human society An algal bloom is a relatively rapid increase in the population of (usually) phytoplankton algae in an aquatic system. ... Variations in CO2, temperature and dust from the Vostok ice core over the last 450,000 years For current global climate change, see Global warming. ...

A counter-hypothesis is advanced in The Revenge of Gaia, the book by James Lovelock. Warming oceans are likely to become stratified, with most ocean nutrients trapped in the cold bottom layers while most of the light needed for photosynthesis in the warm top layer. Under this scenario, deprived of nutrients, marine phytoplankton would decline, as would sulfate cloud condensation nuclei, and the high albedo associated with low clouds. As of 2007 this hypothesis remains speculative. The Revenge of Gaia: Why the Earth is Fighting Back - and How we Can Still Save Humanity (2006) is a book by James Lovelock. ... James Lovelock in front of a statue of Gaia in 2000 Dr James Ephraim Lovelock, CH, CBE, FRS (born 26 July 1919) is an independent scientist, author, researcher, environmentalist, and futurologist who lives in Cornwall, in the south west of Great Britain. ... Water stratification occurs when water of high and low salinity (halocline), as well as cold and warm water (thermocline), forms layers that act as barriers to water mixing. ... The leaf is the primary site of photosynthesis in plants. ... Albedo is the ratio of reflected to incident electromagnetic radiation. ... 2007 is a common year starting on Monday of the Gregorian calendar. ...

See also

• Bergeron process

The Bergeron Findeisen Process is the formation of precipitation in the cold clouds of the mid and upper latitudes by ice crystal growth. ...

References and external links

• R. Charlson, James Lovelock, M. Andreae and S. Warren (1987). Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate. Nature, 326, 655-661.
• Apollo.lsc.vsc.edu
• www.agu.org
• www.grida.no
• Condensation Nucleus National Science Digital Library - Cloud Condensation Nucleus
• DMS and Climate
• Dimethyl Sulfide - Summary
• AGU Association between CCN and Phytoplankton