The agency says it will suspend efforts, in the works for more than 20 years, to develop measures that would allow the agency to enforce bedrock clean air laws at factory farms.By Georgina GustinThe Environmental Protection Agency late last week announced it would end a 20-plus-year effort to develop methods to monitor air pollution from factory farms, effectively shuttering the agency’s stop-and-start attempts to regulate the potentially pollutant-spewing facilities under the Clean Air Act.