Lung Deposited Surface Area of Ambient Fine Particles: Measurement Methodologies and Location-Dependent Characteristics

Exposure to ambient fine particles has strongly been associated with premature deaths as well as with various severe diseases. The health effects of particulate pollution are typically linked to fine particulate matter (PM2.5), which refers to the mass concentration of particles smaller than 2.5 µm. However, an increasing number of studies have reported that monitoring of only PM2.5 is not enough to properly understand the health effects of particulate pollution. For example, PM2.5 seems to be relatively more harmful in lowly polluted regions compared to highly polluted ones. Therefore, additional methods to measure and regulate ambient fine particles are needed to better tackle the health risk caused by particulate pollution.

In this thesis, particle lung deposited surface area (LDSAal) concentrations and characteristics were investigated in different urban environments and countries. The studied environments covered urban traffic sites, highways, detached housing residential areas, airports, shipping and industrial sites in Finland, Germany, Czechia, Chile and India. The measurements were done by utilising a novel LDSAal measurement method, which was developed as a part of this thesis. The thesis aims to answer what particulate emissions are especially relevant in terms of LDSAal, and to what extent the measurement of LDSAal could explain the varying health effects of PM2.5. Also, the thesis aims to improve the overall understanding of LDSAal in terms of its measurement principles and definitions.

In the results of this thesis, it was observed that, in Finland (low PM2.5), LDSAal depended significantly on the urban environment and was strongly attributable to ultrafine particles and black carbon (BC) emissions. Also, in Central Europe (moderate PM2.5), LDSAal was dependent on the ultrafine particles and BC, but, in addition, heavily influenced by the regional aerosol. In Chile and India (high PM2.5), LDSAal was dominated by the regional aerosol despite that the measurements were done at busy traffic sites. The findings of this thesis show potential health-relevant differences in the characteristics of lung-depositing particles near different pollution sources and in different countries. Also, the results indicate that the ratio between LDSAal and PM2.5 increases strongly as a function of decreasing PM2.5 which could potentially explain why PM2.5 seems to be relatively more harmful in areas with low average PM2.5. In all, this thesis highlights the potential of LDSAal as a health-relevant metric for particulate pollution. On the other hand, the results of this thesis also emphasise current challenges related to the commonly used LDSAal measurement principles and definitions.