This paper gives a detailed technical overview on some new sensing technologies for environmental sustainability in the context of the smart cities. COST Action TD1105 EuNetAir is the European networking framework to discuss a research roadmap for new sustainable technologies applied to the air quality monitoring, indoor/outdoor energy efficiency, odour monitoring, CO2 detection for industrial applications, and automotive air quality measurements. The main aim of the concerted Action EuNetAir, funded by COST EU program, is to create an international network of world-class experts in a multidisciplinary approach to define challenging research and innovation needs related to the new sensing technologies for air-pollution and environmental sustainability. The key-technologies for supporting environmental sustainability are the low-cost, low-power and accurate sensors to provide pervasive technologies distributed in the smart cities by engaging citizens' community for enhanced awareness in the clean environment and green energy. These efforts impact on future improved quality of life in Europe supporting green-economy and sustainable development. © 2014 IEEE.