Aerosol Light Scattering Properties: Temporal Variability and the Influence of Relative Humidity
Atmospheric aerosols influence the climate directly by scattering and absorbing incoming radiation and indirectly by altering cloud properties and lifetimes. Hygroscopicity, the ability of aerosol particles to absorb water, strongly impacts their chemical, physical, and optical properties, especially their light scattering potential. Insufficient understanding of aerosol hygroscopic behavior leads to significant uncertainties in estimating their role in climate modeling.
This dissertation investigates the long-term variability of aerosol light scattering and climate-relevant properties across European environments. It also introduces a novel single-nephelometer-based method for measuring light scattering enhancement at elevated relative humidity in an urban environment.
A consistent decline in aerosol light scattering at multiple atmospheric stations suggests a continuous reduction in aerosol mass concentrations. Multi-year analyses from a rural site in the Czech Republic and an urban site in France reveal an increased aerosol cooling potential, likely due to changes in chemical composition and particle size distribution. However, the simultaneous increase in ultrafine particle number concentrations at the urban site raises concerns about the effectiveness of air quality policies, especially regarding human health. The study of aerosol hygroscopicity using the newly developed method shows a notable enhancement of aerosol scattering under humid conditions, even in a heavily anthropogenically influenced environment. These findings provide new insights into urban aerosols’ hygroscopic properties and respective radiative impacts, which are still underrepresented in existing datasets.
The findings of this study contribute to filling the knowledge gap in the characterization of light scattering properties in different environments and their relationship with ambient humidity. The results highlight the need to integrate hygroscopicity measurements into long-term aerosol monitoring networks. Future research should focus on multidecadal trends and ensure that aerosol optical properties are better represented in climate and air quality assessments.