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Abstract: The North Atlantic Oscillation (NAO), a measure of the strength of the zonal wind across the North Atlantic Ocean, strongly influences weather conditions in NW Europe, e.g. temperature, precipitation and wind, especially during winter. It was hypothesised that elevated concentrations of nitrogen oxides in Gothenburg would be enhanced during negative NAO index (NAOI) conditions, representing more anticyclonic weather situations and thus leading to limited air mixing in the urban atmosphere, than situations with NAOI > 0. Hourly wintertime (December–February) concentrations (1997–2006) of NO2, NO, air pressure, temperature and wind direction from an urban rooftop (30 m above street level) in the centre of the City of Gothenburg were analysed in relation to NAOI. Air pressure, the average concentration of nitrogen oxides (NOx = NO2 + NO), as well as the fraction of hourly NO2 and NO concentrations exceeding 90 μg m−3 and the fraction of daily NO concentrations exceeding 60 μg m−3, were significantly and negatively related to NAOI. Air temperature was positively correlated with NAOI. Southerly and westerly winds were more common in months with positive NAOI, while easterly and northerly winds were overrepresented in months with negative NAOI. High pollution concentrations dominantly occurred in situations with northerly and easterly wind directions. High NO2 and NO concentrations were associated with negative NAOI, especially in the morning when the traffic rush coincided with restricted air mixing. Over the ten-year period there were trends for more negative NAOI and increased time fractions with hourly NO2 concentrations exceeding 90 μg m−3. The conclusion of this study is that a climate shift towards higher or lower NAOI has the potential to significantly influence urban air pollution in North-West Europe, and thus the possibility to reach air quality standards, even if emissions remain constant. [Copyright &y& Elsevier]

Abstract: The main aim of this project was to explore whether the pine trees in Glen Affric (GAF), one of the more extensive pine woodlands in the northern Scottish Highlands, are, on average, reaching a senescent stage which could ultimately be detrimental to the sustainability of the pine woodland in this region under present management conditions. This aim was realized by (1) comparing the mean stand age of the GAF trees to other pine woodlands around Scotland, (2) exploring whether there was a significant pre-death trend in ring-width series from naturally dead trees and (3) assessing whether a notable change in response of tree growth to climate was noted as a function of age which could indicate that trees were entering a state of senescence. The average age of the GAF pine trees is 236 (±36) years compared to 225 (±55) years for Scotland as a whole and comparing the GAF data to older pine trees around Scotland suggests that the current mature trees should remain healthy for at least the next century. We also note no significant pre-death trend in ring-width time-series measured from recently dead standing trees. Intriguingly, however, there is a consistent weakening in the response of the pine trees to temperatures through the 20th century. Despite younger trees showing, on average, a stronger response to temperatures, they show the greatest temporal instability in response. This response change is likely not related to tree senescence and ongoing research is exploring this phenomenon in more detail. [Copyright &y& Elsevier]

Nine Scots pine tree-ring-width chronologies were compared regarding growth variability and response to climate along a gradient of oceanicity–continentality at 62–64°N in central Fennoscandia. The study revealed higher growth variance and stronger response to climate in the oceanic area west of the Scandinavian Mountains, compared to the more continental areas further east. However, there was a gradual change in radial tree growth and response to climate along the gradient, where tree growth in a transition zone between oceanic and continental climate showed positive correlations with radial tree growth in both oceanic and continental areas. Pine growth responded positively to summer temperatures in the western areas, and positively to summer precipitation in the east. Generally, pine growth showed a weaker relationship with the North Atlantic Oscillation (NAO) than with temperature and precipitation. During the summer, pine responded to the NAO only in western Fennoscandia, while during the winter pine responded to the NAO in both western and eastern Fennoscandia. This suggests that, during winter, the NAO is an adequate measure for climatic variations important for pine radial growth along the whole studied gradient, while, in the summer, the NAO is an inadequate measure for climatic variations important for pine radial growth east of the Scandinavian Mountains. During the second half of the twentieth century, pine growth in western Fennoscandia displayed reduced sensitivity to climate, while the opposite was found in the east. Indications of growth stress were found in one site east of the Scandinavian Mountains, and, as increasing temperatures have been accompanied by increasing precipitation in Fennoscandia throughout the twentieth century, we suggest that a change in climate regime from subcontinental to suboceanic caused those trees to experience climatic stress. However, trees in either oceanic or more continental areas did not seem to respond negatively to recent climatic change. [ABSTRACT FROM AUTHOR]