Measurement report: New particle formation and aerosol properties at a newly founded atmospheric observatory at the Finnish Baltic Sea coast

Abstract. Aerosol formation is an important contributor to climate in different environments. Coastal ecosystems are of special interest, since their habitat types and species can be highly diverse which can lead to high variability in fluxes of aerosol precursor vapours. Here, we present the first results from an atmospheric observatory established in 2022 at the Tvärminne Zoological Station (TZS) on the southern coast of Finland as a part of the Centre for Coastal Ecosystem and Climate Change Research (CoastClim). This work is focused on new particle formation (NPF) and how it is influenced by the coastal environment. NPF occurred at TZS roughly as often as at the well-established boreal forest site Hyytiälä, 230 km north-north-east of TZS. However, only one-third of the events occurred during the same days at both stations. Similarly to Hyytiälä, NPF events were most likely to be observed when clean air masses from the Norwegian Sea pass over the boreal forest region. To understand the special characteristics of aerosol formation at the coast, we also studied local intermediate ion formation (LIIF), which can tell us about aerosol formation potential in the vicinity of the measurement site. LIIF was more abundant over the continent compared to the marine sector and it was favoured by low condensation sink and sunny dry conditions. This study presents an overview of aerosol size distributions at TZS and provides a basis for future work, which will aim to understand the sources of coastal aerosol precursors and their links to coastal ecology and biogeochemistry.