Occurrence and sources of particulate nitro-polycyclic aromatic hydrocarbons in ambient air in Denmark

The occurrence of selected nitro-polycyclic aromatic hydrocarbons (nitro-PA Hs) associated with atmospheric particulate matter has been investigated at an urban site and at a semi-rural site. For this purpose an analysis metho d based on gas chromatography and tandem ion trap mass spectrometry has bee n developed and applied. The nitro-PAK levels have been compared with level s of other air pollutants including unsubstituted PAHs, inorganic gases and particulate matter, as well as with meteorological parameters. Correlation s and concentration ratios suggest that the dominant source of 9-nitroanthr acene at the urban site is direct emissions, whereas at the semirural site its dominant source is atmospheric formation. The atmospheric formation of 2-nitrofluoranthene and 2-nitropyrene generally seems to be initiated by OH radicals during the day rather than by NO3 radicals at night. The average contribution of the OH initiated formation is estimated to be in the range of 90-100%. However, under wintertime conditions with cloudy weather implyi ng low OH radical production, NO3 radicals may also be important as initiat ors of nitro-PAH formation. Samples influenced by transport of polluted air masses from the European continent have significantly elevated concentrati ons of atmospherically formed nitro-PAHs. The directly emitted nitro-PAHs, 1-nitropyrene and 3-nitrofluoranthene, do not exhibit elevated levels durin g such long-range transport episodes. (C) 2000 Elsevier Science Ltd. All ri ghts reserved.