Recent findings on large nitrous oxide (N 2 O) emissions from permafrost peatlands have shown that tundra soils can support high N 2 O release, which is on the contrary to what was thought previously. However, field data on this topic have been very limited, and the spatial and temporal extent of the phenomenon has not been known. To address this question, we studied N 2 O dynamics in two types of subarctic permafrost peatlands, a peat plateau in Russia and three palsa mires in Finland, including also adjacent upland soils. The peatlands studied have surfaces that are uplifted by frost (palsas and peat plateaus) and partly unvegetated as a result of wind erosion and frost action. Unvegetated peat surfaces with high N 2 O emissions were found from all the studied peatlands. Very high N 2 O emissions were measured from peat circles at the Russian site (1.40 AE 0.15 g N 2 O m À2 yr À1 ). Elevated, sparsely vegetated peat mounds at the same site had significantly lower N 2 O release. The N 2 O emissions from bare palsa surfaces in Northern Finland were highly variable but reached high rates, similar to those measured from the peat circles. All the vegetated soils studied had negligible N 2 O release. At the bare peat surfaces, the large N 2 O emissions were supported by the absence of plant N uptake, the low C : N ratio of the peat, the relatively high gross N mineralization rate and favourable moisture content, together increasing availability of mineral N for N 2 O production. We hypothesize that frost heave is crucial for high N 2 O emissions, since it lifts the peat above the water table, increasing oxygen availability and making it vulnerable to the the physical processes that may remove the vegetation cover. In the future, permafrost thawing may change the distribution of wet and dry surfaces in permafrost peatlands, which will affect N 2 O emissions.

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According to the World Health Organization particulate emissions from the combustion of solid fuels caused more than 110,000 premature deaths worldwide in 2010. Log wood combustion is the most prevalent form of residential biomass heating in developed countries, but it is unknown how the type of wood logs used in furnaces influences the chemical composition of the particulate emissions and their toxicological potential. We burned logs of birch, beech and spruce, which are used commonly as firewood in Central and Northern Europe in a modern masonry heater, and compared them to the particulate emissions from an automated pellet boiler fired with softwood pellets. We determined the chemical composition (elements, ions, and carbonaceous compounds) of the particulate emissions with a diameter of less than 1 µm and tested their cytotoxicity, genotoxicity, inflammatory potential, and ability to induce oxidative stress in a human lung epithelial cell line. The chemical composition of the samples differed significantly, especially with regard to the carbonaceous and metal contents. Also the toxic effects in our tested endpoints varied considerably between each of the three log wood combustion samples, as well as between the log wood combustion samples and the pellet combustion sample. The difference in the toxicological potential of the samples in the various endpoints indicates the involvement of different pathways of toxicity depending on the chemical composition. All three emission samples from the log wood combustions were considerably more toxic in all endpoints than the emissions from the pellet combustion. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1487-1499, 2017.

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