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Ash occurs naturally from any fire that burns vegetation, and may disperse in the soil to fertilise it, or clump under it for long enough to carbonise into coal.
This section needs expansion. You can help by adding to it. (May 2024)
The composition of the ash varies depending on the product burned and its origin. The "ash content" or "mineral content" of a product is derived its incineration under temperatures ranging from 150 °C (302 °F) to 900 °C (1,650 °F).[4]
The composition of ash derived from wood and other plant matter varies based on plant species, parts of the plants (such as bark, trunk, or young branches with foliage), type of soil, and time of year. The composition of these ashes also differ greatly depending on mode of combustion.
Wood ashes, in addition to residual carbonaceous materials (unconsumed embers, activated carbons impregnated with carbonaceous particles, tars, various gases, etc.), contain a between 20% and 50% calcium in the form of calcium oxide and are generally rich in potassium carbonate. Ashes derived from grasses, and the Gramineae family in particular, are rich in silica.[5] The color of the ash comes from small proportions of inorganic minerals such as iron oxides and manganese. The oxidized metal elements that constitute wood ash are mostly considered alkaline.
For example, ash collected from wood boilers is composed of[6]
Strictly speaking, calcium and potassium salts produce the aforementioned calcium oxide (also known as quicklime) and potassium during the combustion of organic matter. But, in practice, quicklime is only obtained via lime-kiln, and potash (from potassium carbonate) or baking soda (from sodium carbonate) is extracted from the ashes.
Other substances such as sulfur, chlorine, iron or sodium only appear in small quantities. Still others are rarely found in wood, such as aluminum, zinc, and boron. (depending on the trace elements drawn from the soil by the incinerated plants).
Ash composition also varies by which part of the tree was burnt. Silicon and calcium salts are more abundant in bark than in wood, while potassium salts are primarily found in wood. Compositional variation also occurred based on the season in which the tree died.
Specific types
Joss paper ash. With wind and dispersion, the size of particulates decreases, while the number of particles increases.
Cremation ashes
Cremation ashes, also called cremated remains or "cremains," are the bodily remains left from cremation.[7] They often take the form of a grey powder resembling coarse sand. While often referred to as ashes, the remains primarily consist of powdered bone fragments due to the cremation process, which eliminates the body's organic materials.[8][9] People often store these ashes in containers like urns, although they are also sometimes buried or scattered in specific locations.[10]
Food ashes
In food processing, mineral and ash content is used to characterize the presence of organic and inorganic components in food for monitoring quality, nutritional quantification and labeling, analyzing microbiological stability, and more.[4] This process can be used to measure minerals like calcium, sodium, potassium, and phosphorus as well as metal content such as lead, mercury, cadmium, and aluminum.
“Burning of joss paper accounted for up to 42% of the atmospheric rBC [refractory black carbon] mass, higher than traffic (14-17%), crop residue (10-17%), coal (18-20%) during the Hanyi festival in northwest China", according to a 2022 study, "the overall air quality can be worsened due to the practice of uncontrolled burning of joss paper during the festival, which is not just confined to the people who do the burning,” and “burning joss paper during worship activities is common in China and most Asian countries with similar traditions.”[13]
This section needs expansion. You can help by adding to it. (August 2024)
Wildfire ash
High levels of heavy metals, including lead, arsenic, cadmium, and copper were found in the ash debris following the 2007 Californian wildfires. A national clean-up campaign was organised ...[14] In the devastating California Camp Fire (2018) that killed 85 people, lead levels increased by around 50 times in the hours following the fire at a site nearby (Chico). Zinc concentration also increased significantly in Modesto, 150 miles away. Heavy metals such as manganese and calcium were found in numerous California fires as well.[15]
This section needs expansion. You can help by adding to it. (August 2024)
“Particles of dust or smoke in the atmosphere are essential for precipitation. These particles, called ‘condensation nuclei,’ provide a surface for water vapor to condense upon. This helps water droplets gather together and become large enough to fall to the earth”[16]
^Pépin, Denis (2013). Composts et paillis: pour un jardin sain, facile et productif. Terre vivante. p. 54. ISBN978-2360980918.
^Couturier, Christian; Brasset, Thierry. "Gestion et valorisation de cendres de chaufferies bois" [Management and recovery of wood boiler ashes] (PDF) (in French). Agence de l'Environnement et de la Maîtrse de l'Energie. Archived from the original(PDF) on 2015-01-15. Retrieved 2024-06-24.
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