a-pinene autoxidation at sub-second time-scales

Atmospheric aerosols impact climate and health. Most of the smallest atmospheric nanoparticles are formed by oxidation of volatile organic compounds (VOC) and subsequent condensation of resulting low-volatile vapors. Biogenic terpenes are the largest atmospheric secondary organic aerosol (SOA) source, and among these, a-pinene likely the single most important compound.

 Recently, autoxidation changed the paradigm of long processing time-scales in the formation of SOA [1, 2]. Previous experiments with cyclic unsaturated compounds have indicated the autoxidation to be very rapid, forming compounds with even 10 O-atoms infused to the carbon structure in a few seconds timeframe [3-6]. Berndt et al. noted that the whole process was apparently finished already at about 1.5 seconds reaction time in cyclohexene ozonolysis initiated autoxidation, indicated by the “frozen” peroxy radical product distribution beyond this reaction time [4].

Here we performed sub-second time-scale flow reactor experiments of a-pinene ozonolysis initiated autoxidation under ambient atmospheric conditions to constrain the timeframe needed to form the first highly-oxidized reaction products, and to inspect the peroxy radical dynamics at significantly shorter reaction times than have been previously possible. The shortest achievable reaction time was around 0.1 seconds and was enabled by the new Multi-scheme chemical IONization (MION) inlet setup [7]. Nitrate and bromide were used as reagent ions in this work.

 

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