Particles sampled directly from the exhaust pipes of a number of vehicles were analyzed using aerosol time-of-flight mass spectrometry （ATOFMS） in real time. Both organic and inorganic chemical species including sodium, calcium, CnHm were observed in individual exhaust particles. Preliminary results suggest that it might be possible to use calcium in combination with more specific organic peaks as a marker for automobile exhaust particles. ATOFMS can also be used as a real-time monitor, characterizing particles produced from vehicles. Furthermore, determination of chemical tracers in individual exhaust particles allows for more accurate source allocation of atmospheric particles.