Alkenes, ketones and aromatic compounds

In the previous chapter, we introduced the OH addition to alkenes. Alkenes are the only class of organic compounds that react in the gas phase with ozone (the often referred DOC decomposition by O3 is almost a result of secondary ROA formation from O3 in solution). This occurs by the addition of ozone, a reaction called ozonol-ysis and has been known for more than 100 years. 

The produced OH and HO2 (as a subsequent product from H) react additionally with the alkenes and provide a huge spectrum of products. Most important is SOA formation (known as a blue haze from biogenic emissions). The stabilized Criegee radical reacts with major species (H2O, SO2, NO, NO2, CO, RCHO and ketones). In the reaction with water vapor direct H2O2 can also be formed (Sauer et al. 1999). 

This is an important source of secondary organic acids. The hydroxyperoxide has been identified as an intermediate. Competing are the following conversions to aldehyde. 

RH-COO -I- (NO, NO2, CO) RCHO + (NO2, NO3, CO2) The reaction with SO2 goes via an adduct, which decays to sulfuric acid. 

Nitrate radicals also react with alkenes by addition, which results in a variety of different compounds such as hydroxynitrates, nitrohydroperoxides and hydrocarbonyls (Wayne et al. 1991). 

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