Mixing state of airborne particles in central Copenhagen and rural background – Particles effective densities for lung dose estimations

Aerosol instruments based on the Differential Mobility Analyzer (DMA) are widely used characterising ambient submicron particle number size distributions. The DMA classifies particles according to their equivalent mobility diameter (dm), which has been shown to be the determining property for the deposition in the respiratory tract, for spherical as well as non-spherical particles (<400 nm, Rissler et al., 2012). In traffic-dense urban environments, soot (black carbon) is often dominating the emissions by mass. The soot cores carry different degrees of coatings (commonly organic). As soon as the particles are emitted to the atmosphere, the atmospheric aging process begins. When estimating exposure, or dose to the lung, with respect to surface area or mass from number size distributions, information about the particle shape and effective density are needed. In this study, mass mobility relationship and particle shape is studied in a traffic-dense urban environment using a DMA-Aerosol Particles Mass analyzer (DMA-APM) technique (Park et al., 2003). From the data the effective density can be determined, defined as: