The existence of pollution externalities calls for government intervention in developing policy measures that will improve social welfare. This paper suggests a method to predict and compare the short-run aggregate output, pollution, and labor input of a competitive industry facing various environmental policies. Assuming that the choice between alternative production technologies can only take place prior to the investment decision, the labor output ratios and the pollution output ratios are fixed in the short run but vary among plants; their distribution is the information used in the aggregation procedure. The performance of different environmental policies--taxes and standards--is examined and compared.