Résumé
The ambient tax is often considered as an efficient instrument to achieve a first best outcome of ambient pollution when the regulator cannot observe individual emissions, or when monitoring costs are prohibitive. While this view is supported to a large extent by experimental findings, there remains several hurdles that hinder the implementation of the ambient tax in the field. One of these hurdles is the nature of the damage. Experimental findings suggest that the efficiency of the ambient tax is higher under external damage, i.e. if ambient pollution affects non-polluters (Spraggon in J Public Econ 84:427-456, 2002) than under internal damage, i.e. if ambient pollution affects polluters themselves (Cochard et al. in Environ Resour Econ 30:393-422, 2005). But this result rests on very different experimental settings. Therefore, we designed a new experiment that allows to compare external and internal damage within a common setting. Our main finding is that the ambient tax is equally efficient under internal and external damage.