Ubiquitous occurrence of 2-nitrofluoranthene and 2-nitropyrene in air

Several nitrated polycyclic aromatic hydrocarbons (nitro-PAH) are direct-acting mutagens and/or carcinogens, and are important constituents of combustion emissions and ambient air. These nitro-PAH are emitted from various combustion sources including gasoline and diesel engine exhaust, aluminium smelting effluent, coal fly ash, wood smoke, and cigarette smoke condensates. Of these, diesel engine exhaust is the best characterized, more than 50 nitrated polycyclic aromatic compounds having been identified by Paputa-Peck et al., including 1-nitropyrene (1-NP) as the single most abundant nitro-PAH. However, nitro-PAH may also be formed during source-receptor transport by atmospheric reactions of adsorbed or gas-phase PAH with oxides of nitrogen, nitric acid and other atmospherically important species such as the OH radical. Evidence for the atmospheric formation of nitro-PAH has come only recently, from observations that 2-nitropyrene (2-NP) and 2-nitrofluoranthene (2-NF) neither of which has been reported to be emitted from combustion sources, are among the major nitro-PAH present in ambient air. We present here data from several locations which demonstrate that these two atmospherically formed nitro-PAH are ubiquitous in tropospheric ambient air.