Relative Humidity Enhancement of New Particle Formation for a Variety of Biogenically - Derived Secondary Organic Aerosol at Atmospherically Relevant Mixing Ratios
AUSTIN FLUECKIGER, Giuseppe Petrucci,
The University of Vermont Abstract Number: 344
Working Group: Aerosol Chemistry
AbstractA significant portion of secondary organic aerosol (SOA) mass in the atmosphere is a direct product of volatile organic compound (VOC) oxidation. Previous studies exploring the impact of relative humidity (RH) on new particle formation (NPF) via ozonolysis of VOCs generally reported a negative correlation of NPF with RH, although some contradictory results exist. Previous studies in our laboratory with respect to α-pinene-derived NPF suggest that, while a modest decrease in NPF is observed at mixing ratios typical of laboratory studies (i.e., > 50 ppbv) at VOC mixing ratios below 10 ppbv, and at an atmospherically relevant RH of 60 %, NPF may, in fact, be enhanced significantly (up to 10-fold). Therefore, the purpose of this study is to examine the potential enhancement of NPF from the ozonolysis of a variety of VOCs (including α-pinene-derived structures) with respect to RH at varying (atmospherically relevant) mixing ratios. Preliminary work with sabinene has shown that at < 1 ppbv mixing ratios, NPF is enhanced under humid conditions compared to dry conditions (0 % RH); this is comparable to α-pinene-derived SOA. In contrast, cis-3-hexenyl acetate (CHA)-derived SOA has shown a shutdown of NPF under humid conditions under all VOC mixing ratio studies. The preliminary work completed in our laboratory suggests the impact of RH on NPF is likely driven by chemical formation, where enhancement or shutdown of particle formation is dependent on the individual VOC. Supporting evidence for chemically driven particle formation is discussed.