NPPC had asked the US Court of Appeals for the District of Columbia Circuit in Washington to review EPA’s decision to regulate emissions of coarse particulate matter (PM), or dust, in rural areas. The organization had argued that while EPA identified problems with coarse PM in urban areas – where it is mostly the byproduct of engine combustion – it failed to show any health effects associated with rural dust, which comes mostly from naturally occurring organic materials such as plants, sand and soil. While recognizing the distinctions between urban and rural PM sources, EPA nonetheless decided to regulate agricultural operations for coarse PM. A 2002 National Academy of Sciences report found that there were no scientifically credible methodologies for estimating emissions from animal feeding operations.

The appeals court accepted EPA’s decision as 'reasonable'. In rejecting arguments from NPPC and other livestock organizations, the court adopted the so-called precautionary principle, placing the burden on the livestock industry to prove that its operations are not harming the public or the environment. The court said, "In assessing the scientific evidence, the [livestock organizations] have mistakenly equated an absence of certainty about dangerousness with the existence of certainty about safety."

Prior to this decision, EPA had the burden of showing there was harm to human health and the environment that needed to be addressed and of explaining why its proposed regulation was necessary to address that harm.

"EPA issued the revised air-quality regulations despite acknowledging that it lacks any science to support imposing them on livestock production operations, and that apparently was okay with the court," said NPPC Environment Committee Chairman Randy Spronk, a pork producer from Edgerton, Minnesota. "More troubling, the court is requiring that we prove a negative.

"We still believe,” Mr Spronk added, “that it simply is inappropriate to treat the naturally occurring emissions from an animal agricultural operation in the same manner as emissions from power plants or refineries."

EPA issued the particulate matter rule in 2006, before a two-year emissions monitoring study of animal feeding operations got underway. The study, which is expected to be completed by January 2010, was part of a 2005 agreement between EPA and the livestock industry. Data from the study is to be used by EPA to develop scientifically credible methodologies for estimating emissions from livestock operations and to promulgate new compliance standards and guidelines. More than 2,700 animal feeding operations, including 1,900 pork farms, signed the so-called 'air consent agreement'.

"Applying this new particulate matter standard to agriculture mandates a solution before deciding if a problem exists," Mr Spronk said.

Under the regulations, livestock operations could be treated as stationary air emissions sources and be required to obtain emissions permits under federal and state laws. As a result, pork production operations could face monitoring for particulate matter such as dust from dirt roads and fields and for chemicals, including ammonia, that can form particulate matter. They also may be subject to Clean Air Act 'new source review' requirements any time a modification or improvement to their operations is made.

"This is a bad decision that will have a profound and long-lasting impact on the struggling American economy," said Michael Formica, NPPC’s chief environmental counsel. “Farmers, business owners, workers and consumers struggling to put food on the table will be harmed by the court’s imprudent decision to use the ‘precautionary principle’ in determining the need for a particular government regulation."