On-line measurements of gaseous nitro-organic compounds in diesel vehicle exhaust by proton-transfer-reaction mass spectrometry

• Emissions of nitro-organic compounds during transient driving cycle were measured.
• Nitromethane and nitrophenol were emitted from diesel vehicle exhaust.
• Nitromethane emission was related with emissions of CO, benzene, and acetone.
• Nitrophenol emission possibly depended on the type of aftertreatment.
• We determined emission ratios of nitromethane to CO, benzene, and acetone.

Nitro-organic compounds, some of which cause adverse health effects in humans, are emitted in diesel engine exhaust. Speciation and quantification of these nitro-organic compounds in diesel engine exhaust particles have been extensively conducted; however, investigations into the emissions of gaseous nitro-organic compounds in diesel engine exhaust have not. In the present study, the properties of gaseous nitro-organic compounds in diesel engine exhaust were investigated through time-resolved measurement with a proton-transfer-reaction mass spectrometer and a chassis dynamometer. Three diesel trucks were tested, each with a different type of exhaust-gas treatment system (i.e., aftertreatment). Among the nitro-organic compounds detected, the emission of nitromethane was commonly observed and found to be related to the emissions of carbon monoxide, benzene, and acetone. The emission of other nitro-organic compounds, such as nitrophenol, depended on the vehicle, possibly due to the type of aftertreatment installed.