	Background

Congressional interest in U.S. energy policy has often focused on ways through which the United States could secure more economical, reliable, and cleaner fossil fuel resources both domestically and internationally. Recent expansion in natural gas production, primarily as a result of new or improved technologies (e.g., hydraulic fracturing) used on unconventional resources (e.g., shale, tight sands, and coalbed methane), has made natural gas an increasingly significant component in the U.S. energy supply. Associated emissions have the potential to contribute significantly to air pollution. The focus of this report is on fugitive and combusted natural gas emissions. Pollutants

Air pollutants associated with natural gas systems include, most prominently, methane and VOCs—of which the crude oil and natural gas sector is one of the highest-emitting industrial sectors in the United States—as well as NO x , SO 2 , and various forms of HAPs. This combustion occurs during several activities, including (1) the flaring of natural gas during drilling and well completions, (2) the combustion of natural gas to drive the compressors that move the product through the system, and (3) the combustion of fuels in engines, drills, heaters, boilers, and other production, construction, and transportation equipment. Hazardous Air Pollutants ( HAP s ). This report summarizes some of the more significant actions taken by EPA, the U.S. Department of the Interior's Bureau of Land Management (BLM), and the U.S. Department of Transportation's Pipeline and Hazardous Materials Safety Administration (PHMSA). EPA and the Clean Air Act

The CAA seeks to protect human health and the environment from emissions that pollute ambient, or outdoor, air. Under the Obama Administration, on August 16, 2012, EPA promulgated new standards for several sources in the "Crude Oil and Natural Gas Production" source category never before regulated at the federal level. On June 3, 2016, EPA promulgated updates to the 2012 standards "for methane and VOC emissions from new and modified oil and gas production sources, and natural gas processing and transmission sources." In a direct response to the Obama-era standards, and in line with his campaign promises, President Trump signed Executive Order 13783 on March 28, 2017. The order—entitled "Promoting Energy Independence and Economic Growth"—requires agencies to review existing regulations and "appropriately suspend, revise, or rescind those that unduly burden" domestic energy production and use. Section 7 of the executive order specifically directs the EPA Administrator to review several regulations related to U.S. oil and gas development, including the agency's methane standards. On July 3, 2017, the U.S. Court of Appeals for the District of Columbia Circuit vacated EPA's administrative 90-day stay, agreeing with arguments that the agency improperly used its authority under CAA Section 307(d)(7)(B) to pause provisions of the rule. EPA promulgated NESHAPs for both the "Crude Oil and Natural Gas Production" and the "Natural Gas Transmission and Storage" sectors in 1999. Under the Obama Administration, on November 18, 2016, BLM promulgated a "Waste Prevention, Production Subject to Royalties, and Resource Conservation" rule, which targets natural gas emissions as a potential waste of public resources and loss of royalty revenue. On October 4, 2017, the U.S. District Court for the Northern District of California granted both motions and ruled against BLM's initial postponement. These activities can affect air quality issues in the downstream sectors of the natural gas supply chain. The Regulatory Role of Federal, State, and Local Governments

Federal regulation of air emissions in the oil and gas industry remains controversial. Covered Sources and Pollutants

The 2012 federal air standards focus primarily on the upstream sectors of the oil and gas industry and cover only some of the pollutants and potential sources of emissions. However, the recent expansion in natural gas production in the United States has given rise to a new set of concerns regarding human health and environmental impacts, including impacts on air quality. BLM rescinded many of the novel requirements of its rule on September 28, 2018.
Natural Gas Systems and Air Pollution
Congressional interest in U.S. energy policy has often focused on ways through which the United States could secure more economical, reliable, and cleaner fossil fuel resources both domestically and internationally. Recent expansion in natural gas production, primarily as a result of new or improved technologies (e.g., hydraulic fracturing, directional drilling) used on unconventional resources (e.g., shale, tight sands, and coalbed methane) has made natural gas an increasingly significant component in the U.S. energy supply. This expansion, however, has prompted questions about the potential impacts of natural gas systems on human health and the environment, including impacts on air quality.
The natural gas supply chain contributes to air pollution in several ways, including (1) the leaking, venting, and combustion of natural gas in the course of production operations; and (2) the combustion of other fossil fuel resources or other emissions during associated operations. Emission sources include pad, road, and pipeline construction; well drilling, completion, and flowback activities; and gas processing and transmission equipment such as controllers, compressors, dehydrators, pipes, and storage vessels. Pollutants include, most prominently, methane (i.e., the principal component of natural gas) and volatile organic compounds (VOCs)—of which the natural gas industry is one of the highest-emitting industrial sectors in the United States—as well as nitrogen oxides, sulfur dioxide (SO2), and various forms of hazardous air pollutants (HAPs).
Federal Air Standards for the Sector
Under the Obama Administration, the U.S. Environmental Protection Agency (EPA) promulgated air standards for several source categories in the crude oil and natural gas sector on August 16, 2012. These standards revise previously existing rules and promulgate new ones to regulate emissions of VOCs, SO2, and HAPs from many production and processing activities that had never before been covered by federal standards (including, most notably, VOC controls on new hydraulically fractured natural gas wells). In an extension of these regulations, and in conjunction with the Obama Administration's Climate Action Plan, EPA promulgated additional rules on June 3, 2016, "to set standards for methane and VOC emissions from new and modified oil and gas production sources, and natural gas processing and transmission sources" not covered by the 2012 rule. Further, the U.S. Department of the Interior, Bureau of Land Management (BLM), promulgated a "Waste Prevention, Production Subject to Royalties, and Resource Conservation" rule on November 18, 2016, to target natural gas emissions on federal and Indian lands as a potential waste of public resources and loss of royalty revenue.
In a direct response to the Obama-era standards, and in line with his campaign promises, President Trump signed Executive Order 13783 on March 28, 2017. The order—entitled "Promoting Energy Independence and Economic Growth"—requires agencies to review existing regulations and "appropriately suspend, revise, or rescind those that unduly burden" domestic energy production and use. Section 7 of the order specifically directs the EPA Administrator and the Secretary of the Interior to review several regulations related to domestic oil and gas development, including EPA's 2016 methane standards and BLM's 2016 waste prevention rule. In June 2017, both EPA and BLM announced plans to postpone the compliance dates for certain sections of the standards, pursuant to the Clean Air Act and the Administrative Procedure Act (APA), while the agencies work through the reconsideration process. On July 3, 2017, the U.S. Court of Appeals for the District of Columbia Circuit vacated EPA's administrative stay of the 2016 methane standards. On October 4, 2017, the U.S. District Court for the Northern District of California ruled against BLM's delay. Both agencies have since proposed rulemakings to revise or rescind requirements of the rules. BLM finalized its revisions on September 28, 2018.
Scope and Purpose of This Report
This report provides information on the natural gas industry and the types and sources of air pollutants in the sector. It examines the role of the federal government in regulating these emissions, including the provisions in the Clean Air Act and other statutes, and EPA's and other agencies' regulatory activities. It concludes with a brief discussion of a number of issues under debate, including
defining the roles of industry and local, state, and federal governments; establishing comprehensive emissions data; determining the proper control of pollutants and sources; understanding the human health and environmental impacts of emissions; and estimating the costs of pollution abatement.