Nanoparticle air pollution in major cities and its origin

Suspended particles with a diameter below 1 μm act as vehicles transporting toxic chemicals into the human respiratory system. It is therefore of interest to record the intensity of these particles and to determine the source from which they were emitted. It is shown that this can be done by simultaneously measuring the light scattering (LS), the photoelectric charging (PC), and the diffusion charging (DC). Particles carrying polycyclic aromatic hydrocarbons (PPAH) are detected by their large PC and are generated in combustion of organic materials whereas particles from other sources only exhibit LS and DC. The fraction of particle mass due to PPAH is independent of location and weather conditions. As an example of an application, we study the nanoscale particles found on motorways in or near various large cities. The sources of the majority of these particles are Diesel motors or cars with defect catalysts. Promising strategies for improving the air quality emerge from these observations.