Measurements of the criegee intermediates and oh radical in alkene ozonolysis

The hydroxyl radical is an important atmosphere oxidant, which controls the chemical lifetimes of many atmospheric trace gases and it is involved in the formation of tropospheric ozone and secondary organic aerosols. Alkene ozonolysis is one of the pathways of producing OH radicals through the generation of Criegee intermediates (carbonyl oxides). Criegee intermediates are removed from the atmosphere through various reactions, which are dependent on pressure and relative humidity. In this work, two model alkenes were used to study the formation of Criegee intermediates and OH radical as a function of pressure, through chamber studies using Infrared spectroscopy. Similarly, the chemistry of Criegee intermediates was studied as a function of relative humidity; hydroperoxides and organic acid products were measured by using Proton Transfer Reaction Mass Spectrometry and High-Performance Liquid Chromatography. Through this work, the yields of stabilized Criegee intermediate and OH radical were found to be 0.39±0.06 and 0.60±0.04 in 2,3-dimethyl-2-butene ozonolysis. The yields of stabilized Criegee intermediate and OH radical were found to be 0.45±0.02 and 0.19±0.01 in ethylene ozonolysis. The pressure dependence measurements suggested an increase in the OH radical yields and a significant decrease in the Criegee intermediate yields, as the pressured was increased. Increasing the relative humidity, increased the production of hydroperoxides and organic acids from the Criegee intermediates. The fate of Criegee intermediates is important because the balance of radicals versus formation of products, influences the chemical composition of the atmosphere, which in turn has implications for climate change and health impacts from air pollutants.