Changes of PM2.5 before and after earliest month of retirement between treatment and control counties
Notes: The figure depicts the time trend of monthly PM2.5 concentrations for the treatment and control counties separately. In the upper graph, the solid line represents the treated counties and the dashed line represents the control counties. The lower graph plots the differences. December 2011 is the month when Watts Bar Fossil Plant in Tennessee shut down. The other four coal power plants shut down later (see Table 1). This figure shows that air quality in the treated counties after the retirement of a nearby power plant was improved, while the air pollution levels in the control cities were similar over time.