The Thermo Scientific Model 5012 MAAP measures the aerosol light absorption properties at 670 nm. It registers the modification of radiation fields in the forward and back hemisphere (at 3 different angles) of a glass-fibre filter caused by deposited particles. The aerosol light absorption coefficient is related with ambient black carbon (BC) concentration by applying a specific attenuation factor. BC is primarily derived from carbonaceous particulate emissions from combustion sources, but includes also dust and inorganic salts. At Chacaltaya data is stored with a one-minute resolution.