The regional and local sources of particle lung deposited surface area (LDSA^al) and aerosol physical and chemical characteristics in a major Central European city

The physical and chemical composition of ambient fine particles is crucial to understand when assessing the adverse health effects of air pollution. Currently, particle health effect estimations as well as air quality monitoring are mainly based on the particle mass (like PM_2.5). However, PM_2.5 cannot be used to assess the effects of ultrafine particles, nor it cannot explain why in some regions PM mass seems to be relatively more harmful. In this study, the detailed physical and chemical characteristics of urban aerosol, together with particle lung deposited surface area (LDSA^al) measurement, were analysed in Düsseldorf, Germany, to understand the aerosol that people are exposed to in a typical large Central European city. Overall, LDSA^al, PM_2.5 and chemical composition were mainly dependent on the regional aerosol, which was linked to aged aerosol as well as traffic and biomass burning within the city. Near pollution hotspots (airport, river, city centre), LDSA^al increased by 14–19 %, whereas PM_2.5 increased by 4–13 %. However, a major fraction of particles were smaller than 10 nm, suggesting potential health effects (like brain effects) without clear contribution to LDSA^al. Particle number concentrations were clearly elevated near the pollution hotspots, especially the airport, showing the importance of non-road-traffic local pollution sources in urban environments. The study highlights the need to control pollution sources both outside and within cities in Central European cities. Also, the need to understand the health-damaging potential of ultrafine particles, including the semi-volatile, non-volatile and sub-10 nm fractions, is emphasised.