The Effect of Changing Background Emissions on External Cost Estimates for Secondary Particulates

This paper discusses the importance of background concentrations of NH3, SO2 and NOx for the estimation of environmental external costs of secondary particulates. A modified version of the ECOSENSE software was developed within the ongoing series of European ExternE projects, devoted to the assessment of energy related environmental exter- nal costs. Using the Windrose Trajectory Model the yearly average concentrations of pollutants at ground level was calcu- lated based on average meteo data and a simple scheme of atmospheric reactions. After this, epidemiological exposure- response functions are applied to determine the impact on the receptors. Finally, the calculated physical impacts are monetized on the basis of selected economic evaluations. The fact that estimates of external costs of incremental emis- sions of NOx and SO2 will increase when background emissions decrease is the most important new result. The choice of relevant background emissions is therefore essential to obtain meaningful estimates of external costs.