Black carbon

Chemically, black carbon (BC) is a component of fine particulate matter (PM ≤ 2.5 µm in aerodynamic diameter). Black carbon consists of pure carbon in several linked forms. It is formed through the incomplete combustion of fossil fuels, biofuel, and biomass, and is emitted in both anthropogenic and naturally occurring soot.0.8 ± 0.4 (2001)1.0 ± 0.5 (2002)»0.7 ± 0.2 (2003) 0.8 (2005) 1.0 arctic Chemically, black carbon (BC) is a component of fine particulate matter (PM ≤ 2.5 µm in aerodynamic diameter). Black carbon consists of pure carbon in several linked forms. It is formed through the incomplete combustion of fossil fuels, biofuel, and biomass, and is emitted in both anthropogenic and naturally occurring soot. Black carbon causes human morbidity and premature mortality. In climatology, black carbon is a climate forcing agent. Black carbon warms the Earth by absorbing sunlight and heating the atmosphere and by reducing albedo when deposited on snow and ice (direct effects) and indirectly by interaction with clouds, with the total forcing of 1.1 W/m2. Black carbon stays in the atmosphere for only several days to weeks, whereas carbon dioxide (CO2) has an atmospheric lifetime of more than 100 years. The term black carbon is also used in soil sciences and geology, referring either to deposited atmospheric black carbon or to directly incorporated black carbon from vegetation fires. Especially in the tropics, black carbon in soils significantly contributes to fertility as it is able to absorb important plant nutrients. Faraday recognized that soot was composed of carbon and that it was produced by the incomplete combustion of carbon-containing fuels. The term black carbon was coined by Tihomir Novakov, referred to as 'the godfather of black carbon studies' by James Hansen, in the 1970s. Smoke or soot was the first pollutant to be recognized as having significant environmental impact yet one of the last to be studied by the contemporary atmospheric research community. Soot is composed of a complex mixture of organic compounds which are weakly absorbing in the visible spectral region and a highly absorbing black component which is variously called “elemental”, “graphitic” or “black carbon”. The term elemental carbon has been used in conjunction with thermal and wet chemical determinations and the term graphitic carbon suggests the presence of graphite-like micro-crystalline structures in soot as evidenced by Raman Spectroscopy. The term black carbon is used to imply that this soot component is primarily responsible for the absorption of visible light. The term black carbon is sometimes used as a synonym for both the elemental and graphitic component of soot. It can be measured using different types of devices based on absorption or dispersion of a light beam or derived from noise measurements. The disastrous effects of coal pollution on human health and mortality in the early 1950s in London led to the UK Clean Air Act 1956. This act led to dramatic reductions of soot concentrations in the United Kingdom which were followed by similar reductions in US cities like Pittsburgh and St. Louis. These reductions were largely achieved by the decreased use of soft coal for domestic heating by switching either to “smokeless” coals or other forms of fuel, such as fuel oil and natural gas. The steady reduction of smoke pollution in the industrial cities of Europe and United States caused a shift in research emphasis away from soot emissions and the almost complete neglect of black carbon as a significant aerosol constituent, at least in the United States. In the 1970s, however, a series of studies substantially changed this picture and demonstrated that black carbon as well as the organic soot components continued to be a large component in urban aerosols across the United States and Europe which led to improved controls of these emissions. In the less-developed regions of the world where there were limited or no controls on soot emissions the air quality continued to degrade as the population increased. It was not generally realized until many years later that from the perspective of global effects the emissions from these regions were extremely important. Most of the developments mentioned above relate to air quality in urban atmospheres. The first indications of the role of black carbon in a larger, global context came from studies of the Arctic Haze phenomena. Black carbon was identified in the Arctic haze aerosols and in the Arctic snow.