Full Description ADOPTED_FROM:CEN/TR 16998:2016 This Technical Report is focused on the presence of nitro- and oxy-PAH compounds in ambient air. It describes how nitro- and oxy-PAH are formed, what typical concentrations are found, what is known about their toxicity, and what sampling and measurement techniques are available. The conclusions of this report are that nitro- and oxy-PAH concentrations are present in the atmosphere in level that are of concern regarding their high toxicity. Information on the presence of these compounds in ambient air is at least as relevant as information about PAH. Validated techniques for the measurement of nitro- and oxy-PAH are available.