The design of optimal climate policy with air pollution co-benefits

This paper develops a model of an optimal regulatory program for greenhouse gases (GHGs) emissions that accommodates the benefits due to reductions of co-pollutants including: sulfur dioxide (SO₂), nitrogen oxides (NO_x), volatile organic compounds (VOC), and fine particulate matter (PM_2.5). Employing per ton damage estimates for the co-pollutants produced by an integrated assessment model, co-pollutant damage estimates per ton carbon dioxide equivalent (CO₂e) are developed for over 10,000 sources of GHGs in the lower 48 states including both transportation sources and electric power generation. For coal-fired electric power generation, the co-pollutant damages are larger in magnitude than recent peer-reviewed estimates of the marginal damage for GHGs. The co-pollutant damage per ton CO₂e varies considerably across source types and source location. The paper estimates the welfare gain from adopting a policy that encompasses the spatially variant co-pollutant damage to be between $1 million and $85 million annually. The range depends on the slope of the marginal abatement cost curve. The paper also shows that a distortionary aggregate emission cap reduces the advantage of differentiated policy. Provided an excessively strict cap, the spatially differentiated policy may reduce aggregate welfare. This result has important implications for GHG policy in the United States; although co-pollutant benefits of abating GHGs have been shown to be significant in magnitude, tailoring climate policy to reflect these source-specific co-benefits is not necessarily socially beneficial. This bolsters arguments for upstream policy designs.