Relating aerosol optical properties to different emission sources at a coastal site in Sweden

Atmospheric aerosols contribute to the largest uncertainty in estimates of the Earth’s global energy balance. Their interactions with sunlight and their ability to affect cloud formation leads to both direct and indirect influence of radiative forcing. The substantial uncertainties associated with aerosol climate effects stem amongst others from the complexity of their sources, composition, and properties. Aerosols in coastal areas present a challenging mix of inorganic and organic particles from diverse sources, making measurements and characterization of their properties in these regions essential. 

This study presents measurements of the optical properties of ambient aerosols on Askö, Sweden, from October 2024 to January 2025. Askö, an island and nature reserve located approximately 80 km south of Stockholm, experiences low levels of local pollution, making it an ideal location for studying marine aerosols. Its location in the Trosa Archipelago, facing the Baltic Sea, also makes it well-suited for investigating the impact of long-range transport from Central and Eastern Europe.

Instruments were placed in a container situated on top of a floating platform near the island. Scattering coefficients, measured with a nephelometer, and absorption coefficients, measured with an aethalometer, were used to calculate Scattering and Absorption Ångström Exponents. The Ångström matrix was used to characterize aerosol types found in the area at different times. The optical data set is further complemented by local meteorological data, particle size distributions, and back trajectory analysis. This combination of data will give valuable insights into aerosol sources at this remote location, the degree of aerosol ageing, and the identification of prevailing emissions sources such as local emissions versus long-range transport of air masses.