Potential of carbon uptake and local aerosol production in boreal and hemi-boreal ecosystems across Finland and in Estonia

Continental ecosystems play an important role in carbon dioxide (CO₂) uptake and aerosol production, which help to mitigate climate change. The concept of “CarbonSink+ potential” enables a direct comparison of CO₂ uptake and local aerosol production at the ecosystem scale. Following this concept, momentary net ecosystem exchange (NEE) and the number concentration of negative intermediate ions at 2.0–2.3 nm (N_neg) were analysed for boreal and hemi-boreal ecosystems across Finland and in Estonia. N_neg can tell us how effectively gaseous precursors associated with biogenic emissions from an ecosystem initiate the new particle formation. Four forests, three agricultural fields, an open peatland, an urban garden, and a coastal site were included, with a focus on the summertime. We compared the NEE and N_neg at each site to the boreal Hyytiälä forest (F-HYY) as it is constituted by the dominant ecosystem type in Finland. N_neg was highest at the urban garden site and lowest at the coastal site. The agricultural fields had higher or similar net CO2 uptake rates and higher N_neg than all studied forests. The median net CO₂ uptake rate of the open peatland was only 31 % of that at F-HYY, while the median N_neg was 77 % of that at F-HYY. The median net CO₂ uptake rate in the urban garden was 63 % of that at F-HYY, implying the importance of urban green areas in CO₂ storage. The coastal site was a minor CO₂ sink. It should be noted that the harvest biomass in agricultural fields is not accounted for in this study. Given the large area of forests in Finland, the forests are the most important ecosystems in terms of their CO₂ uptake and local aerosol formation with regard to helping to mitigate climate warming.