Black carbon physical properties and mixing state in the European megacity Paris

Aerosol hygroscopicity and refractory black car- bon (rBC) properties were characterised during wintertime at a suburban site in Paris, one of the biggest European cities. Hygroscopic growth factor (GF) frequency distribu- tions, characterised by distinct modes of more-hygroscopic background aerosol and non- or slightly hygroscopic aerosol of local (or regional) origin, revealed an increase of the rela- tive contribution of the local sources compared to the back- ground aerosol with decreasing particle size. BC-containing particles in Paris were mainly originating from fresh traf- fic emissions, whereas biomass burning only gave a minor contribution. The mass size distribution of the rBC cores peaked on average at an rBC core mass equivalent diam- eter of DMEV 150 nm. The BC-containing particles were moderately coated (coating thickness 1coat 33 nm on aver- age for rBC cores with DMEV =180-280 nm) and an average mass absorption coefficient (MAC) of 8.6 m 2 g 1 at the wavelength = 880 nm was observed. Different time periods were selected to investigate the properties of BC-containing particles as a function of source and air mass type. The traffic emissions were found to be non-hygroscopic (GF 1.0), and essentially all particles with a dry mobility diameter (D0) larger than D0 = 110 nm contained an rBC core. rBC from traffic emissions was