Investigations of the Chemistry of Secondary Aerosol Formation Using Thermal Desorption Particle Beam Mass Spectrometry

摘要

The chemistry of secondary organic aerosol formation from reactions of normal alkenes withrnozone in dry air in the absence and presence of alcohols and carboxylic acids, and in humid airrnwas investigated in an environmental chamber using a recently-developed thermal desorptionrnparticle beam mass spectrometer. Temperature-programmed thermal desorption of collectedrnaerosol shows that the major products include organic hydroperoxides, peroxides, secondaryrnozonides, and monocarboxylic acids. The hydroperoxides and secondary ozonides are formed inrnthe gas phase by a mechanism involving reactions of alcohols, carboxylic acids, water, orrnaldehydes with stabilized Criegee biradicals generated in the alkene-03 reaction, and thernperoxides (peroxyhemiacetals) are formed by subsequent heterogeneous particle-phase reactionsrnof the hydroperoxides with aldehydes. The peroxidic compounds have very low vapor pressuresrnand are stable on the three-hour timescale of the environmental chamber experiments. However,rnwhen analyzed by gas chromatography these compounds thermally decomposed to more volatilerncompounds, including aldehydes, carboxylic acids, and a few unidentified products. These typesrnof reactions could play a role in atmospheric aerosol nucleation and growth and provide arnmechanism for creating fine-particle organic peroxides, which are of interest because of theirrnpotential for adversely impacting human health.