Sub-23 nm particle emissions: nature and measure
Air quality is one of the greatest challenges of today because of the many sources of pollutant emissions. In the urban area the internal combustion engines play a dominant role on pollution despite the innovative technologies. Great efforts have been paid to reduce NOx and PM as their serious toxicological impact on human health and the environment. Nowadays, the regulation regards only the particles larger than 23 nm, but the attention is shifting towards the sub-23 nm particles because of their large presence at the exhaust of the modern engines and their negative impact on human health. The main challenge of the regulation of these particles is the definition of a proper procedure for their measure. The nature of the sub-23 nm particles is not well understood and their measure is strongly affected by the sampling conditions. The aim of this paper is to provide information on the nature of the sub-23 nm particles in order to define the most suitable procedure for their measure.