Sustainable snow handling
Sammanfattning: Urban snow contains pollution that originates from sources such as atmospheric precipitation, traffic emission, and de-icing chemicals. These pollutants accumulate in the snow during the winter and are released when the snow starts to melt. In Sweden, the municipal organizations are responsible for snow handling within the municipalities and the National Road Administration (SNRA) for snow handling on the main roads. Today, no general guidelines are given for how the municipalities should handle the snow, taking environmental aspects into consideration. To minimize the negative effects from snow handling, the Swedish Environmental Protection Agency presented a snow separation strategy. The purpose of this strategy was to separate urban snow into "heavily"- polluted and "less"- polluted categories. In implementing the strategy, municipalities may see difficulties arise when identifying criteria for "heavily polluted" and "less polluted" snow due to the large variations in snow quality within urban areas. The objective of this thesis was to study the conditions for developing an environmentally sustainable snow handling strategy. The research was carried out in three parts: snow handling strategies, pollutions in urban snow and pollution pathways from urban snow. First of all, a survey was conducted dealing with snow handling strategies used in a number of Swedish municipalities. The results concerning pollution in snow are based on field studies. Snow samples were collected in two Swedish municipalities and along a highway in the northern part of Sweden; the snowmelt process and the influence of road salt were studied through a laboratory experiment. The inventory of snow handling strategies in Swedish municipalities showed that the strategies have not changed much over a ten-year period. A study for the city of Luleå showed that the yearly traffic-related emissions and costs were reduced by increasing the use of local snow deposits. On the other hand, local snow deposits may lead to an increased risk of accidents and to negative local effects, such as delayed growing season, flooding, and drainage problems. Pollutants in urban snow such as metals and polycyclic aromatic hydrocarbons and particles have been studied and a comparison of snow quality in two Swedish municipalities, Luleå and Sundsvall, was made. This comparison showed that total concentrations of copper, lead, and zinc were quite similar for sampling sites with no and low traffic. Because of a longer winter period and a lower average temperature in Luleå, a higher accumulated amount of substances was found in Luleå. Also, the use of salt and warmer and shorter winter periods in Sundsvall resulted, to some extent, in lower average total concentrations in the snow pack, but the results show larger variations throughout the season, which may be harder to predict - an important issue when developing snow handling strategies. A comparison of PAH concentrations showed that the results in this study were, to some extent, lower than the results from other studies of snow quality. The pollutants' pathway from urban snow and the effects on melt water quality when using road salt as de-icing chemical have been studied in a snow-melting experiment. The study shows that the use of salt has the largest effect at the beginning of the melting period when the chloride is transported, resulting in lower pH and an increased transport of dissolved metals. When snow melts, larger particles stay on the ground, while smaller particles, to a greater extent, are transported with the meltwater. A comparison of the transport of particles from snow containing salt or no salt showed that an overall larger amount of particles transported with the meltwater if salt is used as a de-icing chemical in a snow handling strategy. A proposal for establishing standard values is discussed, taking results from Swedish investigations into consideration. A first set of guidelines towards developing a more sustainable snow handling strategy is also proposed, which could, preliminarily, be used by municipalities when developing their snow handling strategies.
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