Requiring more ships that stop in U.S. ports to receive power from the onshore electric grid rather than by burning diesel in onboard generators would be a cost-effective way to improve air quality, reports a team led by Parth Vaishnav of Carnegie Mellon University (Environ. Sci. Technol. 2015, DOI: 10.1021/acs.est.5b04860). When in port, ships commonly use diesel generators to provide necessary power, such as for lights and refrigeration. Supplying ships with power through an electric cable would reduce harmful emissions but require new equipment for ports and ships. California already requires that 50% of ship stops at ports in the state use power supplied from shore; that proportion will rise to 80% in 2020. Vaishnav and colleagues modeled the costs of the retrofits as well as the benefits of air quality improvements—reducing NOx, SO2, CO2, and particulate matter—if the requirements extended nationwide. Depending on assumptions they made about how pollutants disperse and react in the atmosphere, they found that retrofitting one-quarter to two-thirds of vessels would yield a net societal benefit of $70 million to $150 million annually from reducing pollution.