Environmental tax in a green market

We examine the impact of an emission tax in a green market characterized by consumers' environmental awareness and competition between firms for both environmental quality and product prices. The unique aspect of this model comes from the assumption that the cost for an increase in quality is fixed. We show that the emission tax improves welfare, thanks to a decline in pollution and despite an accentuation of product differentiation. The higher the marginal environmental damage is, the higher the optimal tax will be. The optimal tax, however, becomes lower than the marginal damage when the market is not too large. Finally, when marginal environmental damage is not too low, the optimal tax leads to a green product monopoly