General comments

The authors analyzed and presented the net ecosystem exchange (NEE) and the number concentration of negative intermediate ions (N_neg) measurements across sites in different ecosystems. They introduced the novel framework "CarbonSink + Potential" to highlight the importance of boreal ecosystems in the climate system. This framework offers an interesting and new perspective on how boreal ecosystems directly absorb CO2 and indirectly influence the radiation balance, thereby mitigating global warming and climate change.

This topic is both significant and relevant to the scope of Biogeoscience. While the paper is generally well-written, the analysis remains preliminary, and the main argument lacks clarity. I believe further analysis is needed to enhance the overall quality of manuscript. Here are some major comments I have:

1. I suggest that the authors change the way they present the data. Figures 2-4 and Figures 6-8 show two series of data for NEE and N_neg, respectively. I wonder why the authors presented the mean, 25th, and 50th percentiles for NEE (and the 50th and 75th percentiles for Nneg) separately in different panels. There are other effective options, such as box plots or violin plots. Additionally, could you combine the results for the different ecosystems? This could make it easier to see the differences between the ecosystems.
2. It is an interesting approach to consider the role of terrestrial ecosystems as direct carbon sinks and indirect sources of new particle precursors and aerosols. However, the comparison conducted in this study did not integrate these two concepts very well. For example, a recent study by Weber et al. (2024) illustrated this integration effectively. I wonder if the authors could provide an estimation of the relative importance of these two concepts.
3. Most of the analysis in this study is based on the diurnal cycle, but it lacks depth in data interpretation. I suggest conducting further analysis to provide more insights. For example, different ecosystems exhibit distinct terpenoid emission patterns. Many boreal needleleaf forest ecosystems are dominated by monoterpenes (Boy et al., 2022), which are important precursors for particles. However, the fen at the Siikaneva site also has high isoprene emissions (Vettikkat et al., 2023), which could suppress the formation of new particles (Kiendler-Scharr et al., 2009). In addition, Vettikkat et al. (2023) reported high temperature sensitivity of terpenoids. I noticed that meteorological data was mentioned in Section 2.2 of the paper, but I did not see any related analysis. Could the authors incorporate additional analysis using meteorological data? For instance, how does Nneg respond to temperature changes? How do different vegetation components or types affect the NEE and N_neg?

Minor comments:

Line 180: The data periods differ among sites. Although the authors claimed that they would not discuss inter-annual variation, data from shorter periods, especially as short as one year, will still be affected by it, which may affect their diurnal cycles and comparisons with other sites. I think the authors should aware this and demonstrate the potential impact of inter-annual variation on their analysis.

Line 400: I don’t understand the purpose of Figure 9. The error bars represent different percentiles on the x and y axes, and the meaning of the dots is not explained (are they means? medians?). In addition, I expected the authors to discuss the relationship between NEE and N_neg, but this scatter plot does not seem to address that. It is more like putting data together.

Reference

Boy, M., Zhou, P., Kurtén, T., Chen, D., Xavier, C., Clusius, P., Roldin, P., Baykara, M., Pichelstorfer, L., Foreback, B., Bäck, J., Petäjä, T., Makkonen, R., Kerminen, V.-M., Pihlatie, M., Aalto, J., and Kulmala, M.: Positive feedback mechanism between biogenic volatile organic compounds and the methane lifetime in future climates, npj Climate and Atmospheric Science, 5, 72, 10.1038/s41612-022-00292-0, 2022.

Kiendler-Scharr, A., Wildt, J., Maso, M. D., Hohaus, T., Kleist, E., Mentel, T. F., Tillmann, R., Uerlings, R., Schurr, U., and Wahner, A.: New particle formation in forests inhibited by isoprene emissions, Nature, 461, 381-384, 10.1038/nature08292, 2009.

Vettikkat, L., Miettinen, P., Buchholz, A., Rantala, P., Yu, H., Schallhart, S., Petäjä, T., Seco, R., Männistö, E., Kulmala, M., Tuittila, E. S., Guenther, A. B., and Schobesberger, S.: High emission rates and strong temperature response make boreal wetlands a large source of isoprene and terpenes, Atmos. Chem. Phys., 23, 2683-2698, 10.5194/acp-23-2683-2023, 2023.

Weber, J., King, J. A., Abraham, N. L., Grosvenor, D. P., Smith, C. J., Shin, Y. M., Lawrence, P., Roe, S., Beerling, D. J., and Martin, M. V.: Chemistry-albedo feedbacks offset up to a third of forestation’s CO2 removal benefits, Science, 383, 860-864, 10.1126/science.adg6196, 2024.

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

Piaopiao Ke et al.,

This manuscript explained and researched the CO₂ uptake and local aerosol production at different types of stations in Finland. Authors analysed each NEE and N_neg characteristics at each station and compare between them. Introduction is very persuasive and interesting why this study is necessary. However, the way to describe the result of experiments is not kind to the readers. Result was simple and it seems like lack of discussion. I also wonder whether the conclusion gives the answer to the question in the Introduction section. Hopefully authors read the manuscript carefully with reader’s view and revise/describe them explicitly.

Please refer to the attachment here.

Kind regards,