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Free radicals (OH, HO2, RO2 and NO3)

Radicals

  • OH hydroxyl radicals: this compound is primarily produced by photolysis of ozone (O3) and nitrous acid (HONO) and represents the most important atmospheric oxidant. It controls the chemical lifetime of most of the reactive atmospheric trace gases in the atmosphere.
  • HO2 hydroperoxy radicals: these radicals are formed in the reaction of OH with CO, in reactions of RO2 radicals, and by photolysis of formaldehyde; HO2 radicals play an important role in the photochemical formation of tropospheric ozone and they regenerate OH radicals by reaction with NO.
  • RO2 organic peroxy radicals: they are produced by reactions of OH or NO3 with hydrocarbons and play an important role in the photochemical formation of tropospheric ozone and of organic aerosols.

All radicals are hightly reactive and have very short atmospheric lifetimes (from fractions of a second to minutes). The concentrations are extremely small (OH: sub-pptv range; HO2, RO2, NO3 : pptv-range). Accordingly, their atmospheric measurement is extremely difficult..


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