Environmental context. The monitoring of aerosol nanoparticles in the atmosphere is a ‘hot’ topic in environmental management. Such particles in the atmosphere are produced by the combustion of fossil fuels such as in engines. Although they make up only a small percentage of particle total mass, nanosized particles account for more than 90% of the particle number in diesel engine exhaust, and their harmful influences on human health are a serious issue. The system developed in this study has great potential to clarify the origin and behaviour of these aerosol particles more precisely using its online characteristics.

Abstract. Resonance ionisation and laser breakdown time-of-flight mass spectrometry (TOFMS) with particle size selectivity using a differential mobility analyser (DMA) was developed and applied to detect components in nanoparticles. The resonance ionisation and laser breakdown TOFMS method was demonstrated to have a sensitivity of ng m^–3, and was shown to be applicable to nanoparticles using a newly developed standard nanoparticle generator. The developed system was successfully applied to 4-stroke diesel engine exhaust gas to show the mass spectrum patterns measured in 30 and 80-nm particles. The measured spectrum intensities were evaluated to calculate the concentration of organic compounds in nanoparticles, and these values were compared with low-pressure impactor measurement results. The two measurements showed concentrations with the same order of magnitude and the validity of the newly developed TOFMS method was examined using the nanoparticles in the actual diesel gas exhaust.