On Friday, September 2, 2011, the White House directed the Environmental Protection Agency (EPA) to withdraw and reconsider a proposal to strengthen National Ambient Air Quality Standards (NAAQS) for ground-level ozone, the primary ingredient in smog. The announcement marked the first time that the Obama Administration formally returned one of its own agencies proposals, and it could indicate heightened executive scrutiny of forthcoming rules economic impacts. The heart of the , NAAQS set maximum levels for six criteria pollutants at levels necessary to protect public health and welfare, implemented through State Implementation Plans covering a broad range of sources. The ozone NAAQS were last revised in 2008, when the Bush Administration set a primary standard of .075 parts-per-million (“ppm”�) — more lenient than the .06-.07 ppm range recommended by EPA’s Clean Air Scientific Advisory Committee.In response to a lawsuit filed against the 2008 standards, the Obama administration agreed to reconsider the ozone NAAQS in September 2009 and proposed adopting a standard with the .06-.07 ppm range shortly thereafter. EPA held three public hearings on its proposal, and as recently as July 26, 2011, EPA stated that it "look[ed] forward to finalizing this standard shortly.".