Black carbon

Black carbon, commonly known as soot, is a component of fine particulate air pollution (PM_2.5). It is formed by incomplete combustion, for example of wood, waste and fossil fuels, a process which also creates carbon dioxide (CO₂), carbon monoxide, and volatile organic compounds.

Black carbon warms the atmosphere because it is very effective at absorbing light. It exacerbates warming of the air and surfaces in regions where it is concentrated, altering weather patterns and ecosystem cycles.

Black carbon lasts only days to weeks in the atmosphere but has significant direct and indirect impacts on the climate, snow and ice, agriculture, and human health.

Top facts

460-1,500x

Black carbon has a warming impact up to 1,500 times stronger than CO₂ per unit of mass.

12 days

The average atmospheric lifetime of black carbon particles is 4-12 days.

5.8 Mt

About 5.8 million tonnes of black carbon were emitted in 2019.

43%

Household energy accounts for nearly half of global black carbon emissions globally.

Emissions

Black carbon particles are released by the burning of fossil fuels, wood, and other biomass fuels, as well as waste. This process also releases CO₂, carbon monoxide, volatile organic compounds, and organic carbon. The complex mixture of gases and particulate matter that arises from this process is often referred to as soot.

Sources differ significantly region to region. In Asia and Africa residential solid fuels contribute 60-80% of emissions, whereas in Europe and North America diesel engines contribute about 70% of emissions.

Solid fuels and kerosene used to cook, light and heat homes, are responsible for close to half of global anthropogenic black carbon emissions, as well as emitting methane, and other air pollutants.

The main black carbon emitting sectors are:

Household Energy
Transport
Industrial Production
Agricultural Burning
Waste Burning
Fossil Fuels

Black carbon: Main anthropogenic sources (kt)
2019. CEDS database.

Black carbon emissions trends

Black carbon emissions are declining thanks to improved practices in brick manufacturing, reduced open burning in the agriculture sector, improved fuel and vehicle standards, cleaner household energy, better access to finance and technology, and a global push for clean air, and they are expected to continue falling as improvements in efficiency and the electrification of cars and other vehicles continue.

While the curve is bending in the right direction for black carbon emissions, we know we can do more to accelerate their reduction.

Black carbon: Sources of human-caused emissions (kt)
2019. CEDS database.

Black Carbon Impacts

When black carbon particles settle on the surface of snow and ice, they accelerate its melting.

Climate change

Black carbon contributes to warming by being very effective at absorbing light and heating its surroundings. Concentrations of black carbon vary considerably over space and time, so its effects are not seen equally on a global scale.

When suspended in the atmosphere, black carbon contributes to warming by converting incoming solar radiation to heat, in the same way asphalt surfaces create islands of heat in urban areas. Black carbon also influences cloud formation and impacts regional weather and rainfall patterns.

When deposited on ice and snow, black carbon particles reduce surface albedo (the ability to reflect sunlight) and heat the surface. This effect is estimated to have contributed to 0.04°C of warming since 1750. The Arctic and glaciated regions such as the Himalayas are particularly vulnerable to melting as a result.

The effects of black carbon are sometimes masked by co-emitted compounds. Some have a cooling effect on the climate, and the type and quantity of co-pollutants differs according to the source.

Sources that release a high ratio of warming to cooling pollutants represent the most promising targets for mitigation and achieving climate and health benefits in the near term.

Health

Black carbon is a component of fine particulate matter (PM_2.5) air pollution, the leading environmental cause of poor health and premature deaths. These particles are many times smaller than a grain of table salt, can penetrate deep into the lungs, and facilitate the transport of toxic compounds into the bloodstream.

Each year, approximately 4 million deaths are associated with long-term exposure to PM_2.5 air pollution.

PM_2.5 air pollution has been linked to a number of health impacts including premature death in adults with heart and lung disease, strokes, heart attacks, chronic respiratory diseases such as bronchitis, aggravated asthma and other cardio-respiratory symptoms.

Infants and children are also affected. PM_2.5 air pollution is responsible for premature deaths of children from acute lower respiratory infections such as pneumonia. These particles have even been found in the lungs, livers and brains of unborn babies, which can impact early childhood development.

How air pollution affects the body

Deaths and illnesses from air pollution are largely down to tiny, invisible airborne particles, known as particulate matter. These particles contain anything from black carbon, to sulphates to lead.

The smallest particles are the deadliest: PM_2.5particles, which are 2.5 microns or less in diameter, and PM₁₀, which are 10 microns or less in diameter. Human hairs are between 50-70 microns in diameter. These tiny particles bypass the body’s defences and lodge in the lungs, bloodstream, and brain.

Agriculture and ecosystems

Black carbon affects the health of ecosystems in several ways. The fine particles settle on plant leaves and increase plant surface temperature, dim sunlight that reaches the earth, and interfere with rainfall patterns.

Changing rain patterns can have far-reaching consequences for both ecosystems and human livelihoods, for example by disrupting monsoons critical for agriculture in large parts of Asia and Africa.

In combination with tropospheric ozone, black carbon also contributes to over 50 million tonnes of staple crop losses globally each year. Areas with concentrated black carbon emissions stand to gain the most substantial benefits from emissions reductions.

Solutions

The CCAC supports implementation of control measures that, if globally implemented by 2030, could reduce global black carbon emissions by as much as 80%.

Several of these emission reductions could be achieved with net cost savings. Adopting these measures would have major positive co-benefits for public health, especially in the developing world.

Clean cookstoves reduce exposure to black carbon and other air pollutant emissions in households, improving health and women's well-being around the world.

Measures to reduce black carbon emissions can slow near-term warming of the climate, increase crop yields, and prevent premature deaths.

Black carbon’s short atmospheric lifetime, combined with its strong warming potential, means that targeted strategies to reduce emissions can provide climate and health benefits relatively quickly.

Household energy

The world's poorest often rely on crude fuels for cooking, heating, and lighting. Simple technologies can make a huge difference to indoor air pollution, black carbon emissions, and deforestation.

Household energy solutions

Transport

The transport sector is responsible for around 23% of black carbon emissions. Existing technology and higher quality fuel can drastically reduce these emissions.

Solutions for heavy-duty vehicles and engines

Agriculture

Open burning in agriculture produces large amounts of black carbon, but can be easily replaced by no-burn waste management techniques.

Agriculture sector solutions

Waste Management

Open burning of waste is an avoidable occurrence, which can drastically improve local air quality and reduce black carbon emissions through the implementation of integrated waste management systems.

Waste sector solutions