Relationship between aerosol oxidation level and hygroscopic properties of laboratory generated secondary organic aerosol (SOA) particles

Laboratory experiments investigated the relationship between oxidation level and hygroscopic properties of secondary organic aerosol (SOA) particles generated via OH radical oxidation in an aerosol flow reactor. The hygroscopic growth factor at 90% RH (HGF(90%)), the CCN activity (kappa(ORG,CCN)) and the level of oxidation (atomic O:C ratio) of the SOA particles were measured. Both HGF(90%) and kappa(ORG,CCN) increased with O:C; the HGF(90%) varied linearly with O:C, while kappa(ORG,CCN) mostly followed a nonlinear trend. An average HGF(90%) of 1.25 and kappa(ORG),(CCN) of 0.19 were measured for O:C of 0.65, in agreement with results reported for ambient data. The kappa(ORG) values estimated from the HGF(90%) (kappa(ORG,HGF)) were 20 to 50% lower than paired kappa(ORG),(CCN) values for all SOA particles except 1,3,5-trimethylbenzene (TMB), the least hygroscopic of the SOA systems. Within the limitations of instrumental capabilities, we show that differences in hygroscopic behavior among the investigated SOA systems may correspond to differences in elemental composition. Citation: Massoli, P., et al. (2010), Relationship between aerosol oxidation level and hygroscopic properties of laboratory generated secondary organic aerosol (SOA) particles, Geophys. Res. Lett., 37, L24801, doi:10.1029/2010GL045258.