Observation and role of the free radicals NO3, ClO, BrO and IO in the troposphere

An attempt is made to obtain estimates of the average tropospheric abundance of nitrate radicals (NO3) and reactive halogen species (halogen oxide radicals and halogen atoms) on a global scale and thus to quantify their possible impact on the oxidation potential of the troposphere. For that purpose we combine new measurements with data that recently became available. It is found that the integrated formation of the radicals is comparable to that of OH radicals in certain situations. However, it is argued that the effects of these radicals on the oxidation capacity of the troposphere are not necessarily additive. For instance, BrO could be an NO3-scavenger.