| Abstract
| - Fine particles of cholesterol were reacted with ozone under pseudo-first-order conditions in an aerosol bagreactor. Gas-phase ozone was monitored using an ozone meter. Particle size distribution functions weredetermined using a scanning mobility particle sizer, which selected particle sizes for introduction into aphotoionization aerosol mass spectrometer (PIAMS). PIAMS was used to determine the concentration ofcholesterol in the aerosol as a function of reaction time. Dilution corrected rate coefficients were used tocalculate the reactive uptake coefficient for ozone onto cholesterol particles as (2.8 ± 0.4) × 10-6. Uptakewas found to be independent of particle diameter for the sizes studied (100 and 200 nm), suggesting that theuptake is surface mediated. The reaction products were also collected on filters and analyzed by electrosprayionization (ESI) mass spectrometry with both direct infusion and liquid chromatography sample introduction.The main primary reaction products contained one, two, or three oxygens added to the cholesterol moiety.Secondary oligomeric products were also observed, consisting of covalently bound dimers and trimers. Tandemmass spectrometry was used to confirm the expected structures of these compounds. The dimers appear to beacyl hydroperoxides, consistent with a previously reported mechanism for the reaction in a nonparticipatingsolvent. Finally, the magnitude of the uptake coefficient confirms that cholesterol is suitable as a local sourcetracer for source apportionment of ambient organic aerosol.
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