It is important to underline the different character of secondary benefits compared to their primary (warming damage avoidance) counterpart. Most critically, secondary benefits do not depend on climate variables but arise only in connection with greenhouse gas abatement. They occur locally or regionally and do not share the global public good character of greenhouse damages. The question of secondary benefits from carbon abatement should also be distinguished from the more comprehensive issue of the optimal abatement mix with respect to all pollutants. The secondary benefit argument is characterized by an implicit primacy of the greenhouse problem, in that improvements in other areas are seen as welcome side-effects of a global warming policy, but are not considered or sought in their own right. This is not necessarily the ideal way to proceed. Strictly, each pollutant should be taxed in proportion to the environmental damage it causes. If there are interdependencies between them, as is the case with global warming and air pollution, these would have to be reflected in the relative tax rates. The currently considered abatement strategies may then no longer constitute the optimal approaches. Once secondary benefits are taken into account, location will also matter. Unlike greenhouse gases, for other air pollutants it matters where they are emitted. Emission reduction measures should therefore be concentrated to those places where the joint benefit of reducing all emissions is highest.