Exploring the potential for continuous measurement of ultrafine particle mass concentration (PM 0.1 ) based on measurements of particle number concentration above 50 nm ( N 50 )

The real-time automatic and accurate measurement of the mass of ultrafine particles is especially challenging due to their low concentrations and the interferences of larger particles. This work introduces a new method to estimate PM0.1 continuously. Based on the theoretical predictions of a 3-D chemical transport model, PM0.1 and N50 (number concentration of particles with a diameter above 50 nm) can have a very good correlation. This hypothesis is tested in this work by analyzing hourly measurements of size distributions, from different cities in Europe for a year. PM0.1 had a strong spatial and temporal correlation with N50 (R2 > 90%). The line passing through zero had an average slope of 0.16 ± 0.01 × 10−9 µg, for an assumed particle density equal to 1 g cm−3. This suggests that PM0.1 can be, at least in principle, measured indirectly but quite accurately and continuously by measuring N50 with a suitable condensation particle counter.