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The reaction of ozone and isoprene has been studied to examine physical and chemical characteristics of the secondary organic aerosol formed. Using a scanning mobility particle sizer, the volume distribution of the aerosol was found in the range 0.05–0.2 μ m. The aerosol yield was estimated to be 0.01, a value which is a factor of 5–10 higher than previous reports. The aerosol formation is complicated by the presence of minor impurities in the isoprene and the fact that OH‐radicals produced in the ozonolysis can react with isoprene to produce organic aerosol. Without an OH‐radical scavenger present, up to 50% of the observed aerosol comes from the OH channel. A GC‐MS analysis of the products of the composite aerosol showed that two methyl tetrols and 2‐methylglyceric acid are formed which can be attributed to the OH reaction channel. A measurement of the effective enthalpy of vaporization using a volatility differential mobility analyzer found the aerosol to have ΔH eff of −42 kJ mol −1 , a value at the upper end of the range of organic aerosols previously studied. Even with the increased yield found in this study, the ozonolysis reaction probably remains a minor contributor to secondary organic aerosol in PM 2.5 from the atmospheric oxidation of isoprene.
Kleindienst et al. (Mon,) studied this question.