Emission of nitrogen oxides and other air pollutants from the petroleum industry causes concerns regarding impacts on sensitive aquatic and terrestrial ecosystems. In order to optimize strategies for emission reductions according to environmental benefits, an integrated modelling tool has been developed (Environmental Impact Factor for Emissions to Air, EIF-Air). The approach takes into account different emissions to air (nitrogen, sulphur, and organic compounds) and different related environmental impacts based on the concept of critical loads and levels. The model currently takes into account four environmental impacts (acidification of surface waters and soils, nutrient effects on terrestrial ecosystems and vegetation damage from elevated ozone concentrations), but is general in it's formulation and can easily be extended to included other relevant impacts. The approach includes atmospheric dispersion modelling of the emissions, a database for current total deposition and models for the different environmental impacts. Results from three case studies are presented. The first shows that nitrogen emission reductions at an offshore installation in the North Sea have larger environmental benefit than a similar reduction in the Norwegian Sea. In the second case the tool is ised to rank different technology options at a Norwegian onshore petroleum facility. The third case compare the environmental benefits of reducing nitrogen emissions at supply ships compared to offshore installations, showing that measures at ships gives larger benefit per unit nitrogen reduced.


The petroleum industry has emissions to the atmosphere of gaseous pollutants, including nitrogen oxides (NOx), sulphur dioxide (SO2) and volatile organic compounds (VOCs). Atmospheric transport of gaseous pollutants may contribute to environmental impacts long distance (up to several hundred kilometres) from the emission sources, even though the highest concentrations and deposition fluxes are found relatively close to the emission source.

Emissions to air from a single source will contribute to the air concentration and deposition flux in a large area, but typically with quite low concentration or flux compared to the total air concentration and deposition flux. With exception of the immediate vicinity of the emission source, the contribution to the total air pollution level from a given single source is usually small, commonly between less than one and a few percent. This can be challenging when having to prioritize between measures to reduce emissions, as the environmental impacts from a single emission source can be virtually impossible to measure.

A main principle in the development and application of the modelling tool is to combine emissions, deposition as well as environmental impacts in the assessment of a given emission. As a part of the assessment of potential measures, environmental benefits of the reductions are considered in order to implement the best measures from an environmental and socio-economic point of view. Important questions the modelling tool can help answer are: Does an investment for an emission reduction give any environmental improvement, or is it only fulfilling a political goal? Where is the best location to reduce emissions and which measure should be preferred at the actual facility? What is the best solution/measure from a cost benefit point of view? Should the authorities allow for third party measures in order to comply with the best environmentally and socio economic best solution? In order to be able to answer such questions, we developed a method for assessing the environmental benefits of possible emission reduction measures. The method summarizes the environmental improvements in a single factor, called Environmental Impact Factor for Emissions to Air, EIF-Air.

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