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

Abstract. Continental ecosystems play an important role in carbon dioxide (CO₂) uptake and aerosol production, which helps to mitigate climate change. The concept of ‘CarbonSink+ potential’ enables a direct comparison of CO₂ uptake and local aerosol production at ecosystem scale. Following this concept, momentary net ecosystem exchange (NEE) and 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 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 focusing on summertime. We compared the NEE and N_neg at each site to the Hyytiälä forest as it is the dominant ecosystem type in Finland. N_neg was highest at the urban garden and lowest at the coastal site. The agricultural fields had higher or similar net CO₂ uptake rate and higher N_neg than all studied forests. The median net CO₂ uptake rate of the open peatland was only 31 % of that in Hyytiälä, while the median N_neg was 77 % of that in Hyytiälä. The median net CO₂ uptake rate in the urban garden was 63 % of that in Hyytiälä, implying the importance of urban green areas in CO₂ sequestration. The coastal site was a minor CO₂ source. Considering the combined effect of CO₂ uptake and aerosol formation and the large area of forests in Finland, the forests are the most important ecosystems helping to mitigate climate warming.