Emissions of biogenic volatiles from the coastal waters of Gulf of Finland, Baltic Sea.

The dearth of measurements of Volatile Organic Compounds (VOCs) in the marine boundary layer have raised question on how the marine environment is impacted or can impact the overlying atmosphere. VOCs emissions in the interface between air and soil, snow or ocean plays a major role in atmospheric oxidation processes, gas-particle transfer and the formation of secondary organic aerosols. Recent studies indicate that some VOCs produce low volatility vapors through the process of autoxidation (Ehn et al., 2014). These low volatility vapors under atmospheric conditions may rapidly form highly oxygenated molecules (HOMs) which act as important precursor vapors leading to new particle formation (NPF). Extensive studies have been done for the terrestrial VOC fluxes and much less attention has been given to the marine emissions of VOCs (Yu and Li , 2021). Coastal NPF may lead to the formation of coastal/marine clouds, which affect many coastal ecosystem processes and the radiation budget globally. Some of the previous studies in coastal settings have identified biogenic emissions as the main driving factor for the NPF (O'Dowd et al., 2002). Every year extensive cyanobacterial blooms occur in the Baltic Sea region and Finnish water bodies, and these blooms could be a significant source of iodic acid, biogenic sulphuric acid and methane sulphonic acid, and possibly biogenic volatile organic compounds (BVOCs) (Thakur et al., 2022) yet no marine BVOC fluxes field studies have been reported so far from this sector. To understand sea to air emission processes of BVOCs and their role in aerosol formation, we have set up a permanent atmospheric laboratory at the Tvärminne Zoological Station (TZS) on the Finnish coast of the Baltic Sea in 2022, under the project “CoastClim” (https://coastclim.org). The laboratory houses state of the art instrumentation to measure the gaseous composition and aerosol size distribution. The continuous measurement of Dimethyl sulphide (DMS) and monoterpenes at the coast, through proton transfer reaction-time of flight mass spectrometer (PTR-ToF-MS) suggests high emissions during the bloom period in summer (June-August 2023). A field experiment through floating glass chamber flux measurements over the algae and phytoplankton rich waters was also carried out at the coastal site of TZS station from 30th May 2022 to 8th June 2022. The samples were collected in Tenax tubes and analyzed using a thermal-desorption instrument connected to a gas chromatograph (Mäki et al., 2017) with a mass selective detector. The results showed high isoprene fluxes followed by a-pinene and other terpenes. Further investigation on the source and processes of the biogenic VOC emission from the sea surface and oxidation chemistry happening in the air is needed to link these emissions to aerosol formation at the TZS coast. Connecting the coastal emissions to aerosol formation for understanding the impacts of climate change is one of the core aims of our multidisciplinary project “CoastClim”.   O’Dowd et al., 2002: doi:10.1038/nature00775 Ehn, M.et al., 2014 : https://www.nature.com/articles/nature13032 Mäki M.et al, 2017: https://doi.org/10.5194/bg-14-1055-2017. Yu & Li., 2021: https://doi.org/10.1016/j.scitotenv.2021.145054 Thakur, R.C, et al., 2022: doi.org/10.5194/acp-22-6365-2022.