Moderate effects of pollution on health may exert an important influence on labor market decisions. The authors exploit exogenous variation in pollution due to the closure of a large refinery in Mexico City to understand how pollution impacts labor supply. The closure led to an 8 percent decline in pollution in the surrounding neighborhoods. It was found that a one percent increase in sulfur dioxide results in a 0.61 percent decrease in the hours worked. The effects do not appear to be driven by labor demand shocks nor differential migration as a result of the closure in the areas located near the refinery.