Air pollution affects millions worldwide, but one of its most harmful components, black carbon, remains less understood. This guide explains what black carbon is, why it matters for climate and health, and how we can measure it.
Although it represents only a small fraction of total air pollution, black carbon plays a significant role in both climate change and human health. It absorbs sunlight and warms the atmosphere, and contributes to respiratory and cardiovascular problems when inhaled.
Accurately measuring how much black carbon is in the air and identifying its sources can help us design more effective air quality policies.
Black carbon (often abbreviated to BC) is part of a broader group of air pollutants known as carbonaceous aerosols – particles that contain carbon in different forms. Unlike most other aerosols, black carbon is composed almost entirely of pure carbon that absorbs all wavelengths of light and as a result appears black. That is also where it got its name: black carbon.
For an informative and fun explanation of what black carbon is and where it can be found, watch the video below.
Black carbon impacts both the human body and our health, as well as the climate and the atmosphere, accelerating global warming. Let’s see its effects in more details.
Black carbon particles are tiny, often smaller than 2.5 micrometers, allowing them to penetrate deep into the lungs and even enter the bloodstream. This can trigger inflammation and increase the risk of heart and brain diseases.
In the illustration below, you can see that black carbon primarily falls within the “fine” (diameter less than 2.5 μm) particle range. This allows it to bypass the body’s natural defenses in the superior airways. Instead of being filtered out, these microscopic particles travel deep into the inferior airways, ultimately reaching the alveoli – the delicate air sacs where gas exchange occurs. Even more critically, the smallest ultrafine particles can cross the alveolar-capillary barrier directly into the bloodstream. Once in circulation, they can trigger systemic inflammation and contribute to cardiovascular and cerebrovascular diseases, making black carbon a threat not just to respiratory health, but to the entire body.
Illustration caption: Black carbon particles are small enough to bypass natural defenses, enter the bloodstream, and even reach the placenta and fetal organs.
In short:
Pathway: Black carbon particles are inhaled → bypass upper airways → reach deep lungs (alveoli) → enter bloodstream.
Result: This causes local lung irritation and systemic (whole-body) effects, including cardiovascular disease.
But the danger doesn’t stop there. Scientists have discovered that black carbon can reach the placenta during pregnancy and even cross into the baby’s bloodstream. Researchers found thousands of soot particles on the fetal side of the placenta, with higher amounts in mothers exposed to more polluted air. Even more concerning, these particles have been found in fetal organs such as the liver, lungs, and brain during early pregnancy, a critical window for development. This exposure is linked to problems such as low birth weight, premature birth, and long-term health risks. In short, air pollution doesn’t just affect mothers but it can harm babies before they are even born.
Learn more in the sources below.
These combined effects make black carbon an important target for air quality management.
Black carbon is one of the most powerful light-absorbing particles in the atmosphere. Suspended in the air, black carbon particles absorb sunlight and warm the surrounding air, heating the atmosphere. When incorporated into cloud droplets, they reduce the clouds’ ability to reflect sunlight. This alters both local weather patterns and global radiation balance. Global radiation balance is the balance between sunlight coming to Earth and heat leaving Earth, which is what keeps our planet’s temperature steady.
However, black carbon’s most noticeable impact appears when it lands on snow and ice. These surfaces typically reflect most incoming sunlight – a property known as albedo. Fresh snow, for example, has one of the highest albedo values on Earth. But when black carbon particles deposit onto snow or ice, they darken the surface and reduce its reflectivity. Instead of bouncing sunlight back into space, the surface absorbs it, accelerating melting.
In the photo below, you can see dark spots where black carbon has deposited. That is where sunshine will be absorbed instead of being reflected, which will cause melting and a higher surface temperature.
Black carbon deposits on ice in Antarctica
Credit: internal media
This additional absorption of sunlight on ice and snow accelerates melting and contributes to the retreat of glaciers and the loss of Arctic ice cover. It also creates a feedback loop: as snow and ice melt, darker land or water surfaces are exposed, which absorb even more heat and further intensify warming.
Once emitted, particles of black carbon remain in the atmosphere for days to weeks, during which they can travel long distances before being deposited. Our field campaigns have tracked this invisible journey of black carbon to some of the most remote regions on Earth. At Yala Glacier in Nepal, an autonomous BC monitoring station installed by ICIMOD’s Atmosphere team has been collecting long-term data at an altitude of approximately 5,000 meters. These observations help quantify how far black carbon travels and how much it contributes to snow and ice melt in high-altitude regions.
Installation of Aethalometer AE33 at Yala Glacier in Nepal for black carbon concentration measurements
Credit: Suresh Pokhrel
Instruments like the Aethalometer, developed and patented by our company, are widely used to monitor black carbon concentrations also in extreme environments, such as high altitudes.
Understanding how black carbon affects Earth’s reflectivity and where it occurs is key for climate science and policy. Cutting black carbon emissions can quickly improve air quality, slow snow and ice melt, and help fight climate change.
That is why we measure it.
Black carbon, or BC for short, forms during the incomplete combustion of fuels, such as diesel, coal, or wood. In cities, it mostly originates from traffic and domestic heating, while in rural or mountainous regions, it often comes from wood burning.
For residential heating, fuels such as wood, charcoal, and even dried dung (often burned in open fires in rural South Asia) are major sources of black carbon. Similarly, crop residue burning (after harvest, for example) in agriculture, as well as forest fires and wildfires, all produce black carbon.
Different industrial processes also release black carbon in the air. Examples include coal-fired power plants, open burning of waste (including plastics and organic material) but also brick kilns, coke ovens, and other small-scale industries using solid fuels.
A good example of black carbon pollution from wood burning is Loški Potok, a municipality in northeastern Slovenia near the Kočevje region. This forested area with scattered villages mainly uses wood for heating during winter.
Measurements of black carbon were taken there in one of the villages (Retje) and showed extremely high concentrations, primarily emitted by residential wood burning.
Indeed, in the municipality of Loški Potok, domestic heating with biomass accounted for ~80% of black carbon emissions.
Above is an example of black carbon emissions from a wood-burning chimney in a rural forested area, illustrating the impact of residential heating on air quality during winter.
Credit: image is generated by AI for educational and illustrative purposes.
Another important source of black carbon is traffic emissions from liquid fuels such as diesel. Traffic as source of black carbon also includes shipping where marine vessels burning heavy fuel oil contribute to black carbon emissions, especially in remote regions like the Arctic. Also, airports, aircraft engines, ground support equipment, and auxiliary power units burn fossil fuels incompletely, releasing soot particles into the air.
A long-term study measuring diesel car emissions found that newer Euro 6c and 6d engines emit significantly less black carbon than older models. However, the worst offenders, known as super polluters, were still diesel vehicles. Other examples of black carbon emitters, besides diesel cars, are diesel trucks, airplanes, and ships that all result from liquid fuels.
Other examples of black carbon emitters, besides diesel cars, are diesel trucks, airplanes, and ships that all result from liquid fuels.
Knowing where black carbon (BC) comes from, traffic or biomass burning, helps policymakers set priorities. To reduce traffic-related black carbon, we need cleaner vehicles and fuels, while biomass burning calls for better stoves and heating systems. Understanding the share of each source ensures the right measures are taken first, and even just knowing which one is more present provides valuable insight for effective action.
The Aethalometer made by Aerosol Magee Scientific uses light absorption at different wavelengths to identify black carbon sources. Here’s how: black carbon absorbs light strongly, but the rate of absorption changes with wavelength depending on its origin.
To tell whether black carbon comes from traffic or wood burning, we use the Absorption Ångström Exponent (AAE). This value shows how light absorption changes with wavelength. The Aethalometer measures absorption at multiple wavelengths (typically 7 or 9).
Traffic-related black carbon has a low AAE (around 1), meaning its absorption stays almost the same across wavelengths. Black carbon from biomass burning has a higher AAE (around 2), which means it absorbs much more light at shorter wavelengths because it also contains brown carbon. This difference allows the Aethalometer to separate the two sources accurately.
This process, which is called source apportionment, lets us know which source a given black carbon fraction belongs to, improving climate models and guiding targeted mitigation.
Aethalometer is ACTRIS-compliant and widely used in European monitoring networks.
To estimate the air pollution we use the Air Quality Index (AQI), a number between 0 and 500 (500 being the worst quality of air) that tells us how polluted and dangerous for our health the air is. The number is determined by taking into account major known pollutants such as ground-level ozone, particulate matter (PM2.5 and PM10), carbon monoxide, sulfur dioxide, and nitrogen dioxide.
Air quality monitoring usually measures PM2.5, which is the total mass of fine particles smaller than 2.5 micrometers. This is good, however, it doesn’t take into account the differences between particle types, which can have very different effects on health and climate.
A large share of PM2.5 are carbonaceous aerosols, mostly created by human (anthropogenic) activities. Black Carbon (BC) is one of the key components of these aerosols because although it represents only a small amount of PM₂.₅, its health and climate impacts are disproportionately high.
Black carbon is a small part of PM₂.₅, but its health and climate impacts are far greater than its mass.
Research shows that long-term exposure to black carbon is linked to cardiovascular risks and higher blood pressure. Its toxicity can increase when coated with organic compounds in the atmosphere, and elevated levels often occur near heavy traffic or wood burning, especially during winter inversions. Based on these findings, experts recommend that air quality indicators include black carbon and brown carbon in addition to PM₂.₅ to better reflect their harm.
Black carbon is pure carbon soot formed during incomplete combustion of fuels like diesel, coal, and wood. It absorbs sunlight and warms the atmosphere.
It penetrates deep into the lungs and bloodstream, causing respiratory and cardiovascular diseases, and accelerates climate warming by reducing snow and ice reflectivity.
Instruments like the Aethalometer measure light absorption at multiple wavelengths to determine black carbon concentration and its sources.
Traffic emissions, biomass burning, industrial processes, and residential heating are the primary sources of black carbon worldwide.
It absorbs sunlight, warms the atmosphere, and darkens snow and ice surfaces, accelerating melting and contributing to global warming.
| Term | Explanation |
|---|---|
| Aerosol | Tiny solid or liquid particles suspended in air, such as smoke, dust or mist. |
| Aethalometer | An instrument, invented/developed and produced by Aerosol Magee Scientific, that measures how much light aerosol particles absorb, used to determine black carbon levels. |
| Black carbon (BC) | Pure carbon soot formed during incomplete combustion; absorbs sunlight and warms the air. |
| Brown carbon (BrC) | A group of organic particles that appear yellow or brown and absorb light mainly in the blue and ultraviolet range. |
| Carbonaceous aerosol (CA) | Airborne particles that contain carbon, including black and brown carbon. |
| PM2.5 | Particulate matter smaller than 2.5 micrometres, small enough to reach deep into the lungs. |
| Source apportionment | Finding out where black carbon is produced and how much each source contributes. |
As new relevant articles are published, they will be added to this page.
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