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

Abstract

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 (κ ORG,CCN ) and the level of oxidation (atomic O:C ratio) of the SOA particles were measured. Both HGF 90% and κ ORG,CCN increased with O:C; the HGF 90% varied linearly with O:C, while κ ORG,CCN mostly followed a nonlinear trend. An average HGF 90% of 1.25 and κ ORG,CCN of 0.19 were measured for O:C of 0.65, in agreement with results reported for ambient data. The κ ORG values estimated from the HGF 90% (κ ORG,HGF ) were 20 to 50% lower than paired κ 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.