Al Heber, a Purdue professor of agricultural and biological engineering who‘s leading the $14.6 million study, said it will collect two continuous years of emissions data at each site.

"The bottom line is we‘re going to get just a ton of data and I think people all over the country are expecting that — regulators, livestock producers, everybody knows we‘re going to get a lot of good data," he said.

To date, more than 2,600 agreements have been signed with livestock companies that operate about 14,000 swine, dairy, egg-layer and broiler chicken farms in 42 states, said Jon Scholl, EPA Administrator Stephen Johnson‘s agriculture adviser.

"We found that we really don‘t have the level of scientific information and data that‘s needed to make some sound policy calls in this area," Scholl said.

One of the farms is a 20,000-head hog farm about 50 miles northwest of Indianapolis in Carroll County owned by Marion Huffer and his relatives. Huffer said his farm was chosen in part because it‘s only about 30 miles from the main campus at Purdue, which is leading the study.

But some environmental groups aren‘t convinced that the study will produce useful results.

Karla Raettig, a lawyer for the group, questions whether the study‘s sample size — 20 farms out of the 14,000 that have signed onto the compliance agreement — is too small to produce results that will reflect typical emissions from the nation‘s livestock farms.

Heber said the 20-farm study is big enough to produce good science.

"We‘d always like more, but this is going to get us a lot closer to the truth than what we have right now," he said. "It‘s a huge step forward scientifically for understanding farm emissions."