This study presents a new method to measure ultrafine airborne particles down to 2.5 nanometers at high concentrations. By growing the particles into droplets, electrically charging them, and detecting the electrical signal, the system enables accurate and compact measurements of the particle number concentration. This approach is useful for on-board monitoring of vehicle emissions where space is limited and high concentrations are measured.

Exhaust emissions from combustion-based vehicles are negatively affecting human health and our environment. In particular, a small share (< 20 %) of poorly maintained or tampered vehicles are responsible for the majority (60 %–90 %) of traffic-related emissions. The emissions from vehicles are currently not properly monitored during their lifetime. We present a roadside measurement technique, called point sampling, which can be used to monitor vehicle emissions throughout their life cycle.

This work describes the design, calibration, and application of a hygrometer and sampling system, which have been developed and used for water content measurement in experimentally simulated atmospheric icing conditions with relevance in fundamental icing research as well as aviation testing and certification. Together with a general description of water content measurement and accompanying uncertainties, the results of a comparison to reference instruments in an icing wind tunnel are presented.