Measurement report: Optical properties of supermicron aerosol particles in a boreal environment

Abstract. Supermicron aerosol particles (PM1–10; here defined as 1 µm < aerodynamic diameter ≤ 10 µm) play a crucial role in aerosol-climate interactions by influencing light scattering and absorption. However, their long-term trends and episodic significance in boreal environments remain insufficiently understood. This study examines measurements of optical properties and mass of PM1–10 over a 12-year period at the SMEAR II station in Hyytiälä, Finland, focusing on their variability and key drivers. By assessing long-term trends, seasonality, and episodic variability, the study provides new insights into the role of these particles in aerosol-climate interactions. Episodic events, such as pollen outbreaks and dust transport, are identified as major contributors to PM1–10 variability and their role in atmospheric processes. In addition, cascade impactor filters were used to quantify super-PM10 particles (Dp>10 µm), which are not detected by optical instruments, addressing key detection limitations. The findings reveal significant long-term trends and pronounced seasonality in PM1–10 mass and optical properties, emphasizing their importance in boreal environments and their episodic relevance in coarse-mode aerosol characterization.