Alkyl Amines in Boreal Forest and Urban Area

Low-molecular-weight alkyl amines are reactive organic nitrogen compounds that are important precursors in secondary aerosol formation. Atmospheric aerosols have direct and indirect effects on Earth’s climate system. Alkyl amines are emitted from marine and terrestrial ecosystems, agricultural activities and other anthropogenic sources. In terrestrial ecosystems, the quantities in the different parts of an ecosystem and formation processes are not well understood. Alkyl amine soil concentration and biosphere–atmosphere exchange measurements are scarce. The main focus of this thesis is to determine concentrations of alkyl amines in ambient air in boreal forest and urban area, and further identify possible sources and reservoirs of alkyl amines in boreal forest. The main results presented in the thesis consist of a timeseries of gasphase concentrations of alkyl amines measured over several months, concentrations of alkyl amines in the soil and fungal biomass, and an emission estimation based on the measured concentrations. Alkyl amines were studied in two northern latitude environments: in a boreal Scots pine (Pinus sylvestris L.) forest at the SMEAR II station in Hyytiälä and in an urban background area at the SMEAR III station in Helsinki. To quantify ambient air concentrations of alkyl amines in these environments, sample collection and analytical methods were developed. Ambient air concentrations of alkyl amines were measured from May to October 2011 in the forest site and from May to August 2011 in the urban site. The effect of the measured ambient air concentrations of alkyl amines on the local air chemistry was also assessed together with aromatic hydrocarbons and terpenoids. To assess boreal forest soil as a source of alkyl amines, a pot-scale experiment was set up. In the experiment Scots pine seedlings were grown on humus soil collected from the forest site, and the effects of Scots pine and soil organic matter (SOM) degrading enzymes on alkyl amine soil concentrations were studied. In addition, fungal strains common in boreal forest soils were cultured, and the alkyl amine concentrations in the grown fungal biomass were quantified. The role of boreal forest soil as a source or as a sink of atmospheric alkyl amines was studied using a gradient-diffusion approach. In the approach, the soil–atmosphere exchange of selected alkyl amines was estimated. This was done by describing dissolution/volatilisation on water and transport processes, and utilizing the quantified soil and ambient air gas-phase concentrations of the selected alkyl amines found in the studied boreal forest. The gas-phase concentrations of alkyl amines in ambient air were found to be higher in the forest site than in the urban site. In the forest site, the atmospheric concentrations appeared to be linked to soil and vegetation activity based on the seasonal course of the measured alkyl amines. Litterfall, a phenological event, coincides with the concentration maxima of some of the measured alkyl amines. In the pot-scale experiment, the SOM degrading enzymes were found to have no effect on the soil concentrations of alkyl amine while the presence of Scots pine was found to have an effect on the concentrations of some of the measured alkyl amines. The soil concentrations of alkyl amines were found to be lower than those measured from the fungal biomass. The most abundant fungal groups (ectomycorrhizal and saprotrhopic fungi) in the forest soil contained the highest quantities of alkyl amines revealing that fungal biomass may be an important reservoir of alkyl amines in boreal forest soil. Based on the flux estimate, the boreal forest soil was found to act as both a source and a sink of alkyl amines. The direction of the flux was dependent on the studied alkyl amines and environmental conditions in the forest site. Soil pH was found to be one of the most critical factors determining the direction of the flux between the soil and the atmosphere.