What is black carbon?

Black carbon (also referred to as BC) is a component of particulate matter and an air pollutant. It’s highly efficient at absorbing heat and a major element of soot.

Black carbon is formed through the incomplete combustion of fossil fuels and biomass and biofuels. It enters the air as fine particulate (PM2.5).

Black carbon emissions have been identified by some sources as potentially the second largest contributor to climate change after carbon dioxide.¹

Where does black carbon come from?

Primary sources of black carbon include:²

• emissions from diesel engines and vehicles
• residential burning such as wood and coal burning
• agricultural waste field burnings
• forest and vegetation fires.

Black carbon emissions are a year-round concern. Fossil fuel combustion emissions are greater in the winter, while wildfire smoke often generates high concentrations of black carbon emissions in the summer. Black carbon pollutants from wildfire smoke also pose an increasing health risk due to drier and hotter global climate conditions.

Asia, Africa, and Latin America contributed 88 percent of global black carbon emissions in 2015 from open biomass burning and residential solid fuel combustion.³

How does black carbon affect your health?

Black carbon contributes to the negative health impacts posed by PM2.5, including respiratory and cardiovascular effects as well as premature death. Between 2012 and 2014, over 85% of the population of the European Union were exposed to PM2.5 levels that exceeded World Health Organization guidelines.⁴

In a 2019 study published in the Journal of the American Medical Association, PM2.5 was associated in nine causes of death among 4.5 million U.S. veterans.⁵ Causes of death included:

• cardiovascular disease
• cerebrovascular disease
• chronic kidney disease
• chronic obstructive pulmonary disease
• dementia
• type 2 diabetes
• hypertension
• lung cancer
• pneumonia

The study added to the body of knowledge on the dangers of PM2.5, as chronic kidney disease, hypertension, and dementia were previously unassociated with PM2.5 pollution.

The same study found that Black individuals as opposed to non-Black individuals (55 vs. 51 percent) and socioeconomically disadvantaged communities as opposed to counties with higher incomes (65 vs. 46 percent) bore a disproportionate attributable burden of death. 99 percent of the burden of death was associated with PM2.5 levels below Environmental Protection Agency standards.

Over the past decade, the scientific community has attempted to disambiguate the different health effects of different components of PM2.5, including black carbon. However, as of yet, there is insufficient evidence to differentiate these effects, so the present assumption is that many different components contribute to the adverse health effects of PM2.5. Of existing evidence, black carbon is most consistently associated with cardiovascular effects in individuals with pre-existing diseases.⁶

What are black carbon’s environmental effects?

Black carbon as a component of PM2.5 can damage ecosystems and reduce agricultural yield by:

• landing on plant leaves and increasing their temperature,
• altering rainfall patterns
• dimming sunlight reaching the earth

Changing rainfalls can have a profound impact for farmers in regions dependent on monsoon rains. A 2011 study published in the Journal of Climate found that black carbon aerosols reduced rains in southwest India, China, Malaysia, Myanmar, Thailand, and increases rainfall in northern India and the Tibetan Plateau from March through May. In the summer months, parts of India as well as Bangladesh, Myanmar, and Thailand saw reduced rainfall due to black carbon.⁷

Black carbon is becoming increasingly recognized for its previously understated role in contributing to climate change. By some estimates, black carbon vies with methane for contributing the second-highest levels of emissions toward global warming after carbon dioxide.

Black carbon has a direct warming effect through absorbing light and radiating this as heat; it also has severe indirect warming effects in the Arctic. When black carbon settles on snow or ice, it accelerates melting; in this way, black carbon reduces the white space in the Arctic that reflects light away from the Earth, further contributing to warming.

In 2017, the eight-nation Arctic Council pledged to control black carbon emissions and decrease Arctic warming. The countries agreed to constrain emissions to between 25 and 33 percent below 2013 levels by 2025.⁸

Countries that have committed to reducing black carbon emissions include:

• Canada
• Denmark
• Finland
• Iceland
• Norway
• Russia
• Sweden
• The United States

A paper presented at the 2016 Fall meeting of the American Geophysical Union noted that biomass burning emissions, or forest fires, play an underestimated role in global warming models.⁹

The paper focused on black carbon in concentrated biomass burnings taking place in Africa. The study found that black carbon’s physical and optical properties changed as particles entered the atmosphere due to oxidation, coagulation, and condensation. Ultimately, black carbon particles absorb energy and turn that energy into heat, contributing to climate change.

Black carbon has a very short atmospheric life span: it will stay in the air for a matter of days to weeks – unlike CO₂, which remains for over a hundred years. By moving quickly to reduce black carbon emissions, there is a significant opportunity to mitigate climate change and potentially make crucial headway in slowing the melting of the Arctic.

What can we do to reduce black carbon emissions?

In Europe and the United States, a significant portion of black carbon emissions come from on-road and non-road diesel transport. However the biggest contributor in Eastern Europe and the Nordic countries is residential combustion.10 In Europe, 84 percent of black carbon emissions are attributed to transport.

The United States Environmental Protection Agency (EPA) estimates, with existing regulations and retrofit diesel engine programs, that 86 percent of U.S. BC emissions may be eliminated by 2030. However, construction and agricultural equipment in countries such as Norway, Sweden, Denmark, and Greece has been identified as a dominant source of emissions and will require more stringent emission regulations.

Residential heating sources, such as wood burning stoves and fireplaces, greatly impact air quality. Steps that can be taken to mitigate air pollution from these sources include:

• automated pellet stoves with exhaust control technologies
• boilers based on wood-gasification technology
• woodchip/firewood appliances with effective particle separators
• fireplace and wood-burning stove use combined with an air purifier

Despite overall improvements in air quality from regulations and policies set forth by global organizations, the human and financial cost of air pollution is immense for many major cities. See our Cost of Air Pollution counter to learn why clean air is an essential investment into saving lives and creating sustainable financial systems.