Sampling Diesel Engine Particle and Artifacts from Nitrogen Oxide Interactions

The possibility that NO₂ artifactually converts polynuclear aromatic hydrocarbons to biologically active species in diesel particle sampling is explored. NO₂ was injected into dilution air upstream of the exhaust mixing point at varvinq concentra-ting levels with both passenger car and truck driving simulations. Ames test specific activity and nitropyrene levels were seen to increase above base levels when the NO₂ level exceeded 5 to 10 ppm. Extract responses to added NO₂ in transient drivinq appeared to initially increase, then level off above about 20 ppm. It is suggested that some requestering of nitratable orqan-ics may be responsible. Reexposure of filtered particles to diluted gas phase diesel exhaust caused little increase in nitroaromatics or Ames activitv. It appears that NO₂ levels below about 5 ppm are relatively safe from filter artifacts.