Sources of the atmospheric contaminants, 2-nitrobenzanthrone and 3-nitrobenzanthrone

2-Nitrobenzanthrone (2NB) was synthesized by reaction of N2O5 in CCl4 at room temperature and used to determine that the hydroxyl-radical- and nitrate-radical-initiated reactions of gas-phase benzanthrone (Bz) produced 2NB rather than 3-nitrobenzanthrone (3NB), the powerful bacterial mutagen first identified by investigators using bioassay-directed fractionation of diesel emission particle extracts. Analysis of a diesel particle standard reference material (SRM 1975) showed the major NB in the sample to be 3NB. In contrast with the diesel SRM, an archived ambient sample with high levels of 2-nitrofluoranthene (2NF) and 2-nitropyrene, which demonstrated that the air mass sampled had undergone significant atmospheric reaction, contained mainly 2NB and much less 3NB. The 2NF/2NB ratio in the ambient sample was estimated to be 35, consistent with the expected lower gas-phase Bz concentration relative to the gas-phase fluoranthene concentration in ambient air. This work reiterates the need for isomer-specific identification of nitrated polycyclic aromatic compounds (nitro-PAC) when assessing the relative contributions of atmospheric formation reactions versus direct emissions to the nitro-PAC present in ambient air samples.