Monitoring campaigns for addressing quantitative and qualitative characteristics of emitted ultrafine and nano-particles during real operating conditions from waste to energy were performed on a modern plant with a specifi-cally designed instrumental protocol. Results are summa-rized for number concentrations and size distributions of particles during sampling conditions representative of both primary particles at stack flue gas and of those aris-ing from dilution and cooling techniques, for identifica-tion of variations theoretically expected immediately following immissions in the receiving atmosphere.