Industry groups have filed suit against EPA over the Agency's final rule, issued January 15, 2013, tightening annual PM2.5 NAAQS to 12 ug/m3 from the previous level of 15 ug/m3, which was set in 1997. These groups will provide a statement of issues to the U.S. Court of Appeals for the D.C. Circuit by mid-April. However, industry comments during the rulemaking process provide insight into the claims likely to be at issue in these cases. These groups previously stated that the decision to tighten the PM2.5 NAAQS was unlawful, arbitrary, and capricious. The groups stated that there are significant scientific uncertainties regarding the causal relationship between the existing levels of PM2.5 and health effects. Further, these groups argued that the Agency's revised PM2.5 standard is more strict than is necessary to meet the Clean Air Act mandate to set a NAAQS sufficient to protect public health with an adequate margin of safety. EPA disputes these claims, stating that the determination to reduce the PM2.5 NAAQS was reached after exhaustive and detailed review by the Clean Air Scientific Advisory Committee ("CASAC") and the public