Particle lung deposited surface area (LDSAal) size distributions in different urban environments and geographical regions: Towards understanding of the PM2.5 dose–response

[Display omitted] •Characteristic LDSAal size distributions depending on urban environment and country.•Ultrafine particles major contributor on LDSAal in Finland and Central Europe.•LDSAal2.5 per PM2.5 multiple times higher in areas having low PM2.5 level.•LDSAal2.5 per PM2.5 has similar non-linear behaviour as dose–response curve of PM2.5.•New LDSAal2.5 notation indicating deposition region and size range introduced. Recent studies indicate that monitoring only fine particulate matter (PM2.5) may not be enough to understand and tackle the health risk caused by particulate pollution. Health effects per unit PM2.5 seem to increase in countries with low PM2.5, but also near local pollution sources (e.g., traffic) within cities. The aim of this study is to understand the differences in the characteristics of lung-depositing particles in different geographical regions and urban environments. Particle lung deposited surface area (LDSAal) concentrations and size distributions, along with PM2.5, were compared with ambient measurement data from Finland, Germany, Czechia, Chile, and India, covering traffic sites, residential areas, airports, shipping, and industrial sites. In Finland (low PM2.5), LDSAal size distributions depended significantly on the urban environment and were mainly attributable to ultrafine particles (