Particle lung deposited surface area (LDSA al ) size distributions in different urban environments and geographical regions: Towards understanding of the PM 2.5 dose-response.

Recent studies indicate that monitoring only fine particulate matter (PM _2.5 ) may not be enough to understand and tackle the health risk caused by particulate pollution. Health effects per unit PM _2.5 seem to increase in countries with low PM _2.5 , 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 (LDSA ^al ) concentrations and size distributions, along with PM _2.5 , 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 PM _2.5 ), LDSA ^al size distributions depended significantly on the urban environment and were mainly attributable to ultrafine particles (<100 nm). In Central Europe (moderate PM _2.5 ), LDSA ^al was also dependent on the urban environment, but furthermore heavily influenced by the regional aerosol. In Chile and India (high PM _2.5 ), LDSA ^al was mostly contributed by the regional aerosol despite that the measurements were done at busy traffic sites. The results indicate that the characteristics of lung-depositing particles vary significantly both within cities and between geographical regions. In addition, ratio between LDSA ^al and PM _2.5 depended notably on the environment and the country, suggesting that LDSA ^al exposure per unit PM _2.5 may be multiple times higher in areas having low PM _2.5 compared to areas with continuously high PM _2.5 . These findings may partly explain why PM _2.5 seems more toxic near local pollution sources and in areas with low PM _2.5 . Furthermore, performance of a typical sensor based LDSA ^al measurement is discussed and a new LDSA ^al _2.5 notation indicating deposition region and particle size range is introduced. Overall, the study emphasizes the need for country-specific emission mitigation strategies, and the potential of LDSA ^al concentration as a health-relevant pollution metric.
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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