The Impact Pathway Approach
The Impact Pathway Approach (Fig. 1) is a bottom-up approach to achieve an integrated assessment of health and environmental impacts caused by air pollution. It was design to evaluate the impacts of different policy interventions on air quality and its consequences.
Fig. 1: Impact Pathway Approach.
In a first step emission release scenarios are modelled by considering different sources of emissions and respective reduction and control measures. In this step both non-technical and technical measures can be considered. Non-technical measures will cause changes in behaviour and thus influence future activities. Technical measures will change emission factors used for emission modelling. In a second step, the transport of pollutants and their chemical transformation is considered by using dispersion models taking into account meteorological conditions. The outcome of such a model are concentration maps depicting current air quality. Based on these concentration values, health and environmental impacts are modelled by using so-called concnetration-response- or exposure-response-relationships. These formulas describe how the relative risk of different impacts such as cancer, restricted activity days or eutrophication change with increasing concentration in air. By applying these risk factors to background incident rates, health and environmental impacts related to the respective scenario can be assessed. In a final step, these impacts are aggregated to allow for better comparability. Monetary values are in most cases based on willingness-to-pay studies or using a cost-of-illness approach.
EcoSense LE does not implement a full Impact Pathway Approach. Instead, it uses unit costs derived by several model runs which simulate the complete Impact Pathway for different emission scenarios. Based on these runs, unit cost factors describing the impacts and associated costs per tonne of pollutant released. With these unit factors, a first estimation of external impacts of different emission scenarios is possible which gives a rough idea about the order of magnitude of related external costs. For a more detailed analysis, however, it is recommended to use a higher model which implements the full Impact Pathway Approach.