Black Carbon (Brown Clouds)

Primary reference(s)

Ramanathan, V. and G. Carmichael, 2008. Global and regional climate changes due to black carbon. Nature Geoscience, 1:221-227.

Additional scientific description

Black carbon is the sooty black material emitted from gas and diesel engines, coal-fired power plants, and other sources that burn fossil fuel. It comprises a significant proportion of atmospheric particulate matter or PM, which is an air pollutant (US EPA, 2019).

Elevated black carbon concentrations in areas with high solar radiation are a major contributor to the so-called ‘brown clouds’ covering large regions, for instance in Asia. Brown clouds have led to dimming of the Earth’s surface, warming of the atmosphere and perturbation of the hydrological cycle, possibly affecting the monsoon (WMO, 2009).

Black carbon is the product of incomplete combustion of fuels and can be analysed by means of different methodologies. When its light-absorbing properties are measured, soot is referred to as black carbon. When its concentration is measured by thermal-optical techniques, soot is known as elemental carbon (Popovicheva et al., 2010).

Despite intensive efforts in recent decades, no widely accepted standard measurement method exists for determining black carbon or light-absorbing carbon. Real-time black carbon measurements can be performed using optical methods, which measure the absorption of light through a filter collecting airborne particles (Ahmed et al., 2010).

Metrics and numeric limits

Not identified

Examples of drivers, outcomes and risk management

Drivers: Black carbon is formed by the incomplete combustion of fossil fuels, biomass and biofuels. Sources include: mobile sources, particularly dieseldriven road vehicles, nonroad mobile machinery and ships; residential heating in combustion facilities, particularly burning of biomass such as fossil fuel coal and wood; and open biomass burning, forest fires and agricultural waste burning (EEA, 2013).

Black carbon is a major contributor to the fine particulate (PM2.5) burden in the air. It is small enough to be easily inhaled into the lungs and has been associated with adverse health effects. The Near-Road Exposures to Urban Air Pollutants Study (NEXUS), evaluated that peat-burning wildfires release enormous amounts of particulate matter, including black carbon, which has been linked to increased risk of heart failure and respiratory hospital visits (US EPA, 2019).

Air quality monitoring networks: the status of black carbon monitoring in Europe has been reported by the European Environment Agency (EEA, 2013).

Control measures: recommended measures include requiring regular vehicle emissions tests, retirement, or retrofitting; banning or regulating slash-andburn clearing of forests and burning of agricultural waste; requiring shore-basedelectrification/ power of ships, regulating idling at terminals, and mandating fuel standards for ships seeking to dock; banning or regulating the sale of certain fuels and/or requiring the use of cleaner fuels; requiring permits to operate industrial, power generating, and oil refining facilities, and periodic permit renewal and/or modification of equipment; and requiring filtering technology and high temperaturecombustion for existing power generation plants (EEA, 2013).