The variability in Salix BVOC emissions and possible consequences for managed SRC plantations

Willow (Salix spp.) trees have been used commercially since the 1980s to produce renewable energy. Some benefits with these trees are that they can clean soil from heavy metals, reduce the risk of nutrient leakage and eutrophication. They could be an alternative to reduce carbon dioxide emissions from fossil fuel, but they are known to emit high rates of biogenic volatile organic compounds (BVOCs). Many thousands of different compounds are included in this group and they can be divided into terpenes, alcohols, alkanes and esters, to mention a few. These compounds are important. For instance, BVOCs help plants to attract pollinators. They serve as a protection to different kinds of stress, e.g., herbivores, heat and pollutions. Once they are released into the atmosphere, they will be involved in many chemical processes. Hydroxyl radicals, which are known to clean the air from pollutions, are depleted by BVOCs leading to increased lifetime of methane. Emissions of BVOCs could also act as precursors for aerosol formation, which in turn might lead to changes in cloud properties and radiative forcing. Photochemical smog like ozone (O3) is another result of the reactions in the atmosphere where BVOCs are involved, which impairs regional air quality. The reported range of emission rates from Salix is wide. Details about age, canopy position of leaves and how commercially used Salix varieties differ in their emission potentials are lacking, which lead to large errors if modelled emissions are based on too simple assumptions. Therefore, the aim of the work in this thesis was to investigate how the emissions vary with height, age, variety and during the growing season to get more reliable emission rates that can be used in models to better assess the impacts on the regional air quality. Measurements of aerosol formation were conducted to be able to determine the potential particle production near the Salix site. The outcome from the Salix measurements was then combined with BVOC measurements on spruce to assess how an ...