25 years of atmospheric and ecosystem measurements in a boreal forest - Seasonal variation and responses to warm and dry years

• Main Authors: Neefjes, Ivo, Laapas, Mikko, Liu, Yang, Medus, Erika, Miettunen, Elina, Ahonen, Lauri, Quelever, Lauriane, Aalto, Juho, Bäck, Jaana, Kerminen, Veli-Matti, Lampilahti, Janne, Luoma, Krista, Mäki, Mari, Mammarella, Ivan, Petäjä, Tuukka, Räty, Meri, Sarnela, Nina, Ylivinkka, Ilona, Hakala, Simo, Kulmala, Markku, Nieminen, Tuomo, Lintunen, Anna
• Other Authors: Faculty of Science, University of Helsinki, Institute for Atmospheric and Earth System Research (INAR), Department of Geosciences and Geography, Polar and arctic atmospheric research (PANDA), Department of Forest Sciences, Ecosystem processes (INAR Forest Sciences), Viikki Plant Science Centre (ViPS), Forest Ecology and Management, Department of Physics, Global Atmosphere-Earth surface feedbacks, Micrometeorology and biogeochemical cycles, Air quality research group
• Format: Article in Journal/Newspaper
• Language: English
• Published: Finnish Environment Institute 2022
• Subjects: VOLATILE ORGANIC-COMPOUNDS; CLOUD CONDENSATION NUCLEI; SCOTS PINE; INTERANNUAL VARIABILITY; MONOTERPENE EMISSIONS; FEEDBACK MECHANISM; AEROSOL-PARTICLES; FLUX MEASUREMENTS; SIZE DISTRIBUTION; NATURAL AEROSOL; 1181 Ecology; evolutionary biology; 1171 Geosciences; Boreal Environment Research
• Online Access: http://hdl.handle.net/10138/350039

Boreal forests are an important source of trace gases and atmospheric aerosols, as well as a crucial carbon sink. As such, they form a strongly interconnected coupled system with the atmosphere. The SMEAR II station is located in a boreal Scots pine forest in Hyytiala, Finland, and has over 25 years of continuous measurements of atmospheric and ecosystem variables. In this study, we analyse the seasonal variations of trace gases, atmospheric aerosols, greenhouse gases, and meteorological variables, measured at the SMEAR II sta-tion during the past two and a half decades. Several ecosystem and atmospheric variables show seasonal correlations with each other, which suggests seasonal interactions within the climate system that links together ecosystem processes, greenhouse gases, trace gases and atmospheric aerosols. For instance, increased global radiation in summer increases air temperature and consequently affects the plant phenology, which promotes the ecosystem carbon exchange and biogenic volatile organic compound (biogenic VOC) release. This further affects the ambient concentrations of highly oxygenated organic molecules (HOMs) as well as the formation and growth of atmospheric organic aerosols. Organic aerosols subsequently influence aerosol optical properties and, through increased scattering, have the potential to cool the climate. We also discuss the impacts of the warm and dry summers of 2010 and 2018 on the studied variables. For these years, we find a higher-than-average ecosystem primary production especially in June, leading to an increased VOC flux from the forest. The increased VOC flux in turn leads to higher HOM and secondary aerosol concentration in the atmosphere. The latter increases light scattering by atmospheric aero-sol particles and thus leads to climate cooling. The results obtained in this study improve our understanding of how boreal forests respond to climate change. Peer reviewed