In our analytical general equilibrium model where two polluting inputs can be substitutes or complements in production, we study the effects of a tax on one pollutant in two cases: one where both pollutants face taxes and the second where the other pollutant is subject to a permit policy. In each case, we solve for closed-form solutions that highlight important parameters. We demonstrate two important ways that environmental taxes and permits are not equivalent. First, the change in the pollutant facing a tax increase depends on whether the other pollutant is subject to a tax or permit policy. Second, if that other pollutant is subject to a tax, then general equilibrium effects can increase or decrease its quantity (affecting overall welfare). However, when the second pollutant is subject to a permit policy that binds, then welfare is not affected by this spillover effect. Finally, a numerical exercise helps demonstrate these two ways that taxes and permits differ. Using the example of coal-fired power plants, our numerical exercise examines the impacts of increasing a hypothetical carbon tax on the quantity of sulfur dioxide emissions.