Atmospheric aerosol evolution is dominated by oxidation of aerosol components by ozone and hydroxyl radical. Both form products of varying volatility and propagate radical chemistry. Ozonolysis proceeds through an alkene-ozone adduct, the primary ozonide (POZ), which decomposes into a carbonyl + Criegee-intermediate (CI) pair. The exothermicity of ozonolysis leads to CI's with an energy distribution peaked at very high internal energy. The time scale for unimolecular reaction (isomerization/decomposition) controls mechanistic branching ratios in both the gas and condensed phases; because this depends on internal energy, CI dynamics are pressure dependent. Only CI's stabilized by collisions have lifetimes permitting bimolecular reactions. We present studies on the pressure dependence of stabilized CI formation utilizing a hexafluoroacetone scavenger. Increasing pressure or carbon number in linear alkenes increases CI stabilization.

Alkene ozonolysis: Selective scavenger studies of stabilized Criegee intermediates

240th National Meeting (2010)

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