Because human activities emit greenhouse gases (GHGs) and conventional air pollutants from common sources, policy designed to reduce GHGs can have co-benefits for air quality that may offset some or all of the near-term costs of GHG mitigation.  We present a systems approach to quantify air quality co-benefits of US policies to reduce GHG (carbon) emissions. We assess health-related benefits from reduced ozone and particulate matter (PM_2.5) by linking three advanced models, representing the full pathway from policy to pollutant damages.  We also examine the sensitivity of co-benefits to key policy-relevant sources of uncertainty and variability.  We find that monetized human health benefits associated with air quality improvements can offset 26–1,050% of the cost of US carbon policies.  More flexible policies that minimize costs, such as cap-and-trade standards, have larger net co-benefits than policies that target specific sectors (electricity and transportation). Although air quality co-benefits can be comparable to policy costs for present-day air quality and near-term US carbon policies, potential co-benefits rapidly diminish as carbon policies become more stringent.

Noelle E. Selin (MIT Engineering Systems Division, 77 Massachusetts Ave. Cambridge, Massachusetts 02139, USA;  MIT Department of Earth, Atmospheric and Planetary Sciences, 77 Massachusetts Ave. Cambridge, Massachusetts 02139, USA)