Two ambient air samples, both collected in a northern latitude city during winter daytimes, are compared here with regard to NO2-AR/PAH levels and OH-NO2-AR levels from filter and XAD-2 extracts. Detection of a previously unreported environmental constituent, tentatively identified as a NO2-azulene isomer, is discussed. The levels of the OH-NO2-AR were, in general, at least 4 times higher than levels of the corresponding NO2-AR. As with NO2-AR/PAH, OH-NO2-AR appear to be both primary source emissions and secondary photochemical products. The filter-collected para-substituted OH-NO2-AR in these samples appear to be the source emissions, while the XAD-collected ortho- and para-substituted OH-NO2-AR may be products of photochemical reactions. Other pollutant and meterological data, including NO, NO2, HONO, sunlight intensity and fine-particle Pb and K concentrations, are also used to discuss differences between these samples. (Copyright (c) 1992 Pergamon Press Ltd.)