The objective of the project is, for the first time, to bring SI traceability to field of black carbon measurements, so that their accuracy and value is greatly increased. The specific objectives are: To establish a set of well-defined physical parameters, such as aerosol light absorption coefficients and mass absorption coefficients, which together can be used to quantify black carbon mass concentrations with traceability to primary standards. To develop and characterise a black carbon standard reference material (SRM), as a near-black carbon source that is highly relevant for atmospheric aerosols, together with methods for using it to calibrate field black carbon monitors. To develop a traceable, primary method for determining aerosol absorption coefficients at specific wavelengths that are to be defined for the benefit of users. The method should have defined uncertainties and a quantified lowest detection limit. To develop a validated transfer standard for the traceable in-field calibration of established absorption photometers such as multi angle absorption photometers, aethalometers and particle absorption photometers. The transfer standard should make use of the black carbon SRM (developed in objective 2) and associated portable instrumentation characterised by the primary method (from objective 3). To facilitate the take-up of the technology and measurement infrastructure developed in the project by standards developing organisations (CEN, ISO) and end users (e.g., European Environment Agency (EEA), World Meteorological Organisation-Global Atmosphere Watch (WMO-GAW), the ACTRIS (Aerosols, Clouds, and Trace gases Research InfraStructure Network) Project).