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This series aims at the measurement of flame generated nanoparticles and an assessment of their biological effects. In the present part a brief review is given on previous papers dealing with nanoparticles with emphasis on detection through various methods. A more detailed account is provided of own measurements using photo ionization mass spectrometry. This includes photo fragmentation, spectra of low pressure flames, coagulation effects, and nanoparticle measurements in the exhaust gas of a sooting normal pressure premixed flame well outside of the visible zone. A model on nanoparticle formation is discussed as are its implications on emissions of vehicle engines.

Abstract. Based on photoionisation mass spectrometry two types of experiments were carried out. (i) In a fast flow reactor coupled to a low pressure flame as a particle source, rate coefficients for the coagulation of primary nanoparticles were measured through variation of the reactor residence time. The results are kc (350K) = 3.5x10-10cm3/s and kc (573K) = 1.1x10-9cm3/s, i.e. very high rate coefficients. It was also shown that coagulated nanoparticles can have masses beyond 50ku, corresponding to equivalent diameters between 4 to 5nm. These particles are easily fragmented during photoionisation. (ii) Using a second and mobile photoionisation mass spectrometer equipped with a fast flow inlet system, measurements were carried out behind three different vehicle engines, a two-stroke scooter engine, a four-stroke motorbike engine and a DI (direct injection) gasoline research engine. In all cases ion signals around 1000u were found that are clearly dependent on engine conditions. In the case of the DI engine, they correlate with the smoke number. These signals cannot be explained by PAHs due to their low volatility at the respective masses. Major contributions of soot or droplet fragmentation were ruled out through additional experiments using a heated inlet line and a filter. Consequently, these signals are interpreted as fragments of coagulated nanoparticles.