The Journey from Forest Emissions to Clouds: Aerosol aging impact on cloud microphysics

This study investigates how biogenic volatile organic compound (BVOC) emissions from boreal forests shape aerosol evolution and subsequent cloud formation, with a focus on the vertical pathway of air parcels and repeated cloud processing. Using long-term aerosol observations from SMEAR II (Finland), we characterize how aerosol size distribution and chemical composition evolve during atmospheric transport and aging. These observations are used to drive simulations with the PseudoAdiabatic bin-micRophySics University of Exeter Cloud parcel model (PARSEC) to assess impacts on cloud droplet activation, supersaturation, and cloud albedo.

We examine how forest emissions influence aerosol growth, composition, cloud condensation nuclei efficiency, and, therefore, cloud microphysics. Particular focus is placed on the role of vertical transport and precipitation processing in shaping aerosol–cloud interactions. The long-term observations reveal that the longer aerosols spend over forests, the more they grow and change in composition. Our simulation results then show that these changes in BVOC-driven aerosol properties impact droplet activation, cloud formation, and cloud microphysic highlighting how BVOC-emission and aerosol aging impact cloud responses.

These findings emphasise the need to represent not only surface emissions but also the full atmospheric processing pathway of aerosols in climate models, especially when assessing the climatic role of forested regions. This study will lead to a comparison between Tropical and Boreal ecosystems impact on aerosol aging and the difference in cloud responses.