Wyoming on Monday asked the 10th U.S. Circuit Court of Appeals to deny challenges from environmental groups to its federally approved plan for controlling nitrogen oxides (NOx), or haze.

State Attorney General Peter Michael asked the court to deny the appeal by a combination of conservation groups that include the Powder River Basin Resources Council, National Parks Conservation Association and the Sierra Club. The U.S. Environmental Protection Agency (EPA) has approved the majority of Wyoming’s regional haze implementation plan, including most of the plan’s steps for dealing with NOx.

The appeals court consolidated three cases, including Wyoming v. EPA.

Gov. Matt Mead called the groups’ arguments “disingenuous,” pushing for “the most strict NOx controls at extraordinary cost that make little perceptible difference” for the state’s plan. “This argument is about visibility conditions, and Wyoming’s plan ensures progress.”

The state’s latest filing stressed that regional haze is caused mostly by sulfur dioxide (SO2) and particulate matter (PM) with NOx making up a relatively small part of the problem. EPA has approved Wyoming plans for SO2 and particulates; the 10th Circuit has upheld the SO2 plan, and the PM plan was not challenged.

In the filing, the state said it is uncertain how much of a role oil and natural gas emissions play in the haze problem.

“Based on these scientific uncertainties and the existing control requirements, Wyoming did not require oil/gas sources to install additional controls during this 10-year implementation period,” the state filing said. “Was EPA wrong to approve Wyoming’s judgment?”

The filing said Congress granted broad authority to the states in determining the best retrofit technology to use and in determining its level of effectiveness, and EPA has no real authority to override the state’s plan.

The EPA faces a $60 million budget cut under the spending bill passed by Congress earlier this month to fund the federal government through Sept. 30 (see Daily GPI, Dec. 16). President Obama signed the legislation on Tuesday.

In addition, the brief argued that there are natural causes, such as wildfires, and sources of haze in adjoining states and countries that make it difficult to control levels of haze in the state.

Even with this lack of total control over the problem, Wyoming’s regional haze plan “nonetheless ensures reasonable progress toward the national visibility goal,” the filing said.