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).