soot

Soot is a black or very dark brown powder produced by the incomplete combustion of hydrocarbon fuels. It consists mainly of carbonaceous material, with adsorbed organic compounds, and is a subset of particulate matter known as black carbon. Soot forms when fuel is not fully oxidized in flames, engines, or other high-temperature combustion processes, leading to tiny carbon-rich particles and their aggregates.

Common sources include diesel and gasoline engines, coal- and biomass-burning power plants, residential heating with solid fuels, kerosene lamps, cooking fires, and wildfires. Primary soot particles are typically submicron in size (often tens to a few hundred nanometers) and frequently assemble into fractal-like aggregates. They are generally insoluble in water and can carry polycyclic aromatic hydrocarbons and other adsorbed compounds on their surfaces.

Health and environmental impacts are significant. Inhaled soot can penetrate deep into the lungs and contribute to respiratory and cardiovascular problems, particularly for vulnerable populations. Environmentally, soot absorbs sunlight, contributing to atmospheric warming and climate change. Deposition on snow and ice reduces albedo and accelerates melt. Soot can be transported long distances, linking air quality across regions.

Monitoring and control efforts focus on reducing emissions of fine soot particles. Measurements often target PM2.5 mass and black carbon concentration. Mitigation strategies include advanced combustion technologies, diesel particulate filters, scrubbing and filtration systems, and the use of clean-burning stoves and fuels. Soot has historical uses as a pigment, such as lampblack, but its contemporary relevance is primarily as a pollutant and climate-active aerosol.

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