Timothy B Onasch — Aerodyne Research, Inc.
Paul Davidovits — Boston College
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Andrew Thomas Lambe — Aerodyne Research, Inc.
Adam Thomas Ahern — Aerodyne Research, Inc.
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Category
Aerosol Properties
Description
HGF and CCN activity as a function of OH exposure for SOA generated by oxidation of α-pinene, m-xylene, 1,3,5-trimethylbenzene, and α-pinene/m-xylene mixtures.
Hygroscopic growth factors (HGF), ethanol growth factors (EGF), and cloud condensation nuclei (CCN) activity were measured for OH-oxidized soot aerosol and secondary organic aerosols (SOA) generated from common gas-phase biogenic and anthropogenic SOA precursors (α-pinene, m-xylene, 1,3,5-trimethylbenzene, and α-pinene/m-xylene mixtures). The species were oxidized in a laboratory aerosol flow reactor at OH radical concentrations that were varied from 4x10^8 molec cm^-3 to 1x10^10 molec cm^-3. The residence time in the flow tube was 120 sec; this combination of OH concentration and transit time (i.e., oxidant exposure) corresponds to 0.5 to 14 days assuming a 24-hour average OH concentration of 1x10^6 molec cm^-3. An Aerodyne aerosol mass spectrometer (AMS) was used to measure bulk aerosol chemical composition, which provided a measure of aerosol oxidation state. Hygroscopic and organic tandem differential mobility analyzers (HTDMA, OTDMA) were used to measure growth factors of oxidized aerosols. The HTDMA measures HGF by passing dry aerosols through water-humidified air (90% relative humidity) and measuring the wet-to-dry particle diameter ratio. The HTDMA therefore provides a measure of water-soluble organic compounds in the aerosol. The OTDMA measures EGF by passing dry particles through ethanol-laden air (80% relative to saturation of ethanol), providing a measure of water-insoluble organics. HGF in the range of 1.0–1.3 and EGF in the range of 1.1–1.3 were measured. The figure displays sample data showing that HGF and CCN activity are strongly correlated with extent of OH oxidation. These results suggest that model parameterizations between aerosol oxidation state, water solubility, and cloud-forming potential are possible.
* Fourteen scientists from 5 institutions participated in the study. Only a partial list of authors is provided in this abstract; a full list of authors is shown on the poster.
