SoREmi

Soil Reactive Emissions from boreal forests (SoREmi): impact of site and soil properties, and effects on atmospheric chemistry

The overall aim of this project is to identify and quantify currently unknown reactive boreal forest soil emissions with the help of analytical methods and total reactivity measurements and link them to tree stand characteristics, and soil properties. A special attention will be drawn to the effects of a warming climate, e.g., environmental factors, and to their impact on atmospheric processes.

Motivation

In our study of the ambient OH reactivity in the boreal forest at the SMEAR II site in Hyytiälä, Finland, we measured surprising high total OH reactivity values in the spring (Praplan et al., 2019). Previous studies at the same time were conducted for short periods of a few weeks in the summer (Sinha et al., 2010; Nölscher et al., 2012). In our study, values for July were similar to the previous studies, but lower than the ones found in the spring.

We noticed that the high values were observed as the soil was thawing in spring. Note that our sampling inlet was located only about 1.5 m above ground. However, we were unable to identify the compounds that might have caused the increase of total OH reactivity during that period.

Therefore, our hypothesis is that reactive compounds are produced in the lower layers of soil and remain "trapped" there during the winter and get released when the soil temperature starts to increase in the spring. While this might be only relevant locally for a short period of time, the fact that we were unable to identify chemically the compounds responsible for the increase in reactivity points towards a potential explanation for the observed missing reactivity at that site and in general in forested areas (see the review by Yang et al., 2016, and the modelling study by Ferracci et al., 2018).

 

The project

 

This project, funded by Academy of Finland (decisions 348013 and 348014), is a consortium between the Finnish Meteorological Institute (FMI) and the Natural Resources Institute Finland (LUKE). I, Dr. Arnaud P. Praplan (FMI), act as consortium PI and Doc. Aino Smolander (LUKE) as subproject PI. Furthermore, the project includes collaborations with colleagues at FMI and LUKE, as well as with the University of Helsinki, the Swedish University of Agricultural Sciences, and the University of Copenhagen.

 

It is a 4-year project (September 2022 - August 2026) with several objectives, briefly summarized here:

• First, we aim at improving our analytical methods to identify the chemical composition of the emissions, in particular nitrogen- and sulfur-containing compounds. A screening will be performed with various boreal forest soils for the broadest possible identification of compounds. If possible, the emissions of the various soil layers (e.g. litter, humus layer) and microorganisms will be analysed separately as well. Finally, reactivity measurements will be performed in order to test again the comprehensiveness of the chemical identification of the emissions.
  
  
• Secondly, we want to link these emissions to soil properties and environmental conditions (e.g. drying/wetting, freezing/thawing, tree species in the stand, age of the stand, different harvest intensities, and with/without nitrogen fertilization). With these results, we aim at developing a parametrization of the emissions that can be used in modelling efforts.
  
  
• Finally, we are interested in the atmospheric impacts of these soil emissions. We will investigate their formation potential of secondary organic aerosol experimentally and estimate their regional or global effect using a global chemistry transport model.

I will report here and on social media about the progress of the project.

References

• Ferracci, V., Heimann, I., Abraham, N. L., Pyle, J. A., and Archibald, A. T. (2018). Global modelling of the total OH reactivity: investigations on the “missing” OH sink and its atmospheric implications, Atmos. Chem. Phys., 18, 7109–7129. doi:10.5194/acp-18-7109-2018.
  
• Nölscher, A. C., Williams, J., Sinha, V., Custer, T., Song, W., Johnson, A. M., Axinte, R., Bozem, H., Fischer, H., Pouvesle, N., Phillips, G., Crowley, J. N., Rantala, P., Rinne, J., Kulmala, M., Gonzales, D., Valverde-Canossa, J., Vogel, A., Hoffmann, T., Ouwersloot, H. G., Vilà-Guerau de Arellano, J., and Lelieveld, J. (2012). Summertime total OH reactivity measurements from boreal forest during HUMPPA-COPEC 2010, Atmos. Chem. Phys., 12, 8257–8270. doi:10.5194/acp-12-8257-2012.
• Praplan, A. P., Tykkä, T., Chen, D., Boy, M., Taipale, D., Vakkari, V., Zhou, P., Petäjä, T., and Hellén, H. (2019). Long-term total OH reactivity measurements in a boreal forest, Atmos. Chem. Phys., 19, 14431–14453. doi:10.5194/acp-19-14431-2019.
  
• Sinha, V., Williams, J., Lelieveld,  J., Ruuskanen, T.M., Kajos, M.K., Patokoski, J., Hellén, H., Hakola, H., Mogensen, D., Boy, M., Rinne, J., and Kulmala M. (2010). OH Reactivity Measurements within a Boreal Forest: Evidence for Unknown Reactive Emissions, Environ. Sci. Technol., 44, 6614-6620. doi:10.1021/es101780b.
• Yang, Y., Shao, M., Wang, X., Nölscher, A.C., Kessel, S., Guenther, A., and Williams, J. (2016). Towards a quantitative understanding of total OH reactivity: A review, Atmos. Env., 134, 147-161. doi:10.1016/j.atmosenv.2016.03.010.