Long term ecosystem fluxes of BVOCs over a Norway spruce (Picea abies) forest in southern Sweden

Abstract

Spruce forests cover a large portion of northern Europe, where species like Norway spruce (Picea abies) is considered to be a significant biogenic volatile organic compound (BVOC) emitter to the atmosphere. BVOCs are highly reactive and can significantly influence atmospheric chemistry. Terpenoids are the most abundant group of BVOCs where especially Monoterpenes can facilitate the formation and growth of secondary organic aerosols (SOA). Additionally, while individual trees are known to change their emission patterns in response to stress factors (e.g. heat stress and drought), there is limited knowledge about how these changes are reflected at an ecosystem level. Despite the widespread presence of these forests, current modelling techniques for predicting BVOC emissions and their influence on radiative forcing are largely based on short-term measurements from chamber measurements. These techniques are widely used as the approach of capturing long-term emission variability along with seasonal patterns poses significant challenges.

This study presents a long-term analysis of BVOC emissions and concentrations from March- November 2023 above a managed Norway spruce forest in southern Sweden. The main objectives were to compare emissions across different seasons and link these emissions patterns with weather observations to also see transportation possibilities, by employing data collected by a PTR-TOF-MS coupled with an eddy covariance method. The findings showed that, overall, emissions can be predicted by an algorithm that has considered PAR and canopy temperature, however, inconsistencies emerged at higher temperatures and PAR with both under- and overestimations. Along with the possible transportation of compounds, it is important to consider how atmospheric circulation might distribute these emissions. Seasonal patterns of emissions and O3 concentrations revealed a correspondence to changes in temperature and light, providing insight into the interactions between BVOC emissions and atmospheric chemistry. Specifically, higher temperatures, increased light levels and increased levels of O3 were associated with increased emissions. This further suggests a strong link between these environmental factors and the production of atmospheric compounds.

Popular Abstract

Norway spruce (Picea abies) forests are common across northern Europe, while they typically are recognized for their beauty and ecological importance, they also play an important role in shaping our atmosphere as they release invisible gases into the air, known as biogenic volatile organic compounds (BVOCs). While they are not visible to the human eye, they are highly reactive and play a key role in air chemistry as they influence air quality and climate. BVOCs are diverse, but one particular group of BVOCs are called terpenoids, these are especially important because they can help form tiny airborne particles that influence cloud formation and how sunlight is reflected or absorbed by the surface of the Earth. Known is that individual trees can release more of these gases when stressed, for example by heat or drought, but there is still much to learn about how entire forests behave over long periods. Most studies on BVOCs rely on short-term measurements, leaving a gap in understanding the long-term patterns of seasonal trends and environmental factors driving these emissions.

In this study, BVOC emissions were monitored from a managed Norway spruce forest in southern Sweden over several months, from March to November 2023. Using advanced techniques and instruments like the eddy covariance method, emissions were tracked, how they varied across the season, and how they were affected by sunlight, temperature, and weather patterns. This resulted in higher emissions when it was warmer, sunnier, or with extreme weather events. What also was discovered in this study was that existing prediction methods sometimes over- or underestimated the emissions. This research highlights the importance of long-term studies to better understand how forests contribute to air chemistry and climate dynamics. By linking emission patterns to environmental factors, we can improve climate models and better predict forests’ impact on air quality, cloud formation, and future climate.

• author: Arnsteg, Alexandra
• supervisor: Thomas Holst
• organization: Dept of Physical Geography and Ecosystem Science
• course: NGEM01 20241
• year: 2024
• type: H2 - Master's Degree (Two Years)
• subject: Earth and Environmental Sciences
• keywords: BVOC, Norway spruce, temperature, SOA, O3, PAR, Planetary boundary layer
• publication/series: Student thesis series INES
• report number: 685
• language: English
• id: 9181092
• date added to LUP: 2025-01-15 10:19:34
• date last changed: 2025-01-15 10:19:34