Report guidance to produce eBC concentrations from NRT ACTRIS absorption measurements

This report pictures the methodology established to produce equivalent black carbon mass concentration (eBC) in near real-time (NRT) from absorption coefficients measured by online monitors, such as the Multi-Angle Absorption Photometer (MAAP) or the various Aethalometer models (e.g., AE33) installed at fixed observatory platforms. These instruments are referred here as Filter Absorption Photometers (FAPs).

As previously defined in the frame of pre-ACTRIS research studies (Petzold et al., 2013): when using FAPs, “equivalent black carbon (eBC) should be used instead of black carbon for data derived from optical absorption methods, together with a suitable MAC [i.e., Mass Absorption Efficiency, in m²/g] for the conversion of light absorption coefficient into mass concentration”.

The process followed within CAMS2.21a to determine such a suitable MAC value at the European scale has been described in milestone M21a.1.1.1 (2023). It notably resulted from the collaborative work of an ad hoc working group of European experts, before discussion was enlarged as also part of WP1 activities of the HE RI-URBANS project, considering synergies between this ACTRIS-related program (proposing and testing services for urban air quality) and CAMS2.21a. This whole process was also conducted in collaboration with the current activities of the European standardization body for ambient air quality on the establishment of equivalent methods for the measurement of elemental carbon deposited on filters (CEN/TC 264 working group 35, chaired by JP Putaud).