Air pollution in European cities is still threatening human health, even though EU emission directives have been sharpened over the last 25 years. Adverse health effects of airborne particles are strongly linked to their size. A major fraction of outdoor ultrafine particles is traffic generated from road, rail, air, and sea transportation. The story that nPETS aims to communicate is the life of the sub 100 nm emissions from its creation to its potential path to human beings and animals. The nPETS consortium aims to improve the knowledge of transport generated exhaust and non-exhaust nanoparticle emissions and their impacts on health and new public policies. It aims to monitor and sample with state-of-the-art particle instruments the sub 100 nm transport generated emissions from shipping, road, rail, and aviation both in field and controlled laboratory environments. Both aged and fresh aerosols will be considered, including primary and secondary volatile and non-volatile particles. Characterising the emissions will be done from shipping, road, rail, and aviation by linking their sizes, chemical compositions, and morphologies to its specific emission sources such as engines, brakes, clutches, and tyres to increase the understanding of the mechanisms behind adverse risks posed by different types and sources of the identified sub 100 nm particles. The effects of nanoparticles from various transport modes and fuels, as well as specific emission sources, will be compared with a focus on markers of relevance for carcinogenesis and inflammation. Living cells will be exposed to collected and real-world primary and aged aerosols as well as primary and aged aerosols generated in the laboratory. Furthermore, it also aims to evaluate the possible future impact of new policies in this area on public health and linking the impacts with specific emission sources. This should lead to an understanding and quantification of the risks posed by different types and sources.