When ozone pollution skyrocketed in the tiny town of Boulder, Wyo., in 2008, it was relatively easy to identify the culprit as oil and gas drilling, the only major industry in the rural area. Today, a similar situation in San Antonio, Texas, will be more difficult to resolve. The city has violated federal ozone standards dozens of times since 2008, but with so much industrial activity in and around the city, local officials are waiting for the results of a state-funded study to pinpoint the source of the pollution.