The measurement of particles in air characterised as black carbon is important both for their role in climate change and as a measure of combustion products associated with health effects. Measurements are made very widely, and compact, precise, real-time, relatively inexpensive instruments are available. Although it is conceptually a simple measure of the light absorbing properties of airborne particles, the metric does not currently have SI traceability, with consequences for the comparability and interpretation of data. The project will provide a workable solution to this major problem, with widespread benefits across the worlds of both climate change and air quality.



The quantity of airborne particles loosely described as black carbon has been widely measured by various optical methods since the early 20th century, because instruments for this are relatively simple and reliable. The dominant sources have changed over the decades, from domestic and industrial coal burning to vehicle combustion emissions, with more recent contributions from wood-burning.

Black carbon has been identified as the second most important climate forcing agent behind CO2, contributing an amount of radiative forcing nearly 30 % that of current CO2 concentrations. Airborne particles have serious human health effects across Europe and worldwide. In 2011, about 430,000 premature deaths in the EU were attributed to fine particulate matter (PM). Studies suggest that black carbon is a better indicator of harmful particulate substances from combustion sources than PM mass concentration.

Although black carbon measurement is in principle a simple optical measurement of absorption, characterised by the aerosol light absorption coefficient, traceability is hampered by the fact that routine monitors determine the absorption of particulate matter collected on a fibrous filter. Empirical but non-traceable correction factors are then incorporated into the conversion from light absorption coefficient into the reported particle mass concentration.