NGA ISSUE BRIEF: Natural Gas & the Environment

  • Natural gas is the cleanest of the fossil fuels, with substantially lower emissions of nitrous oxide, sulfur dioxide, and carbon dioxide.
  • With its positive environmental profile, gas has been the "fuel of choice" for power generation in the Northeast.
  • Natural gas can also play a positive role in reducing transportation and building sector emissions.
  • The natural gas industry is striving to reduce its environmental impacts, through such cooperative efforts as the U.S. EPA's "Natural Gas STAR" program.
  • Natural gas production-including shale gas development-can be conducted in an environmentally sensitive manner, and yield environmental benefits to society.
  • Methane emissions have declined in the U.S. over the last 2 decades, thanks to industry efforts and line replacements to repair leaks. Reducing methane emissions going forward is a common government and industry goal.

Natural gas is a low carbon fuel, and is seen as a key element in U.S. efforts to transform its energy system to be more efficient and environmentally positive. Natural gas has been the "fuel of choice" for power generation in the Northeast for the last decade in large part because of its positive impacts on air quality and the environment; and it is also seen as a positive environmental fuel for transportation and other sectors. A review of some environmental trends regarding natural gas is provided in this summary.

Environmental Advantages of Natural Gas

Natural gas is composed primarily of methane. As described by U.S. EPA: "Natural gas is a fossil fuel formed when layers of buried plants and animals are exposed to intense heat and pressure over thousands of years. The energy that the plants and animals originally obtained from the sun is stored in the form of carbon in natural gas."

Natural gas has far fewer emissions of sulfur, nitrogen and carbon than other fossil fuels such as coal and oil. For instance, compared to coal, natural gas produces half as much carbon dioxide, less than a third as much nitrogen oxides, and virtually no sulfur oxides at the power plant.

Natural Gas and Power Generation

Natural gas has been the dominant fuel for new power generation in the Northeast and nationally for over a decade, and one of the leading reasons has been its beneficial impact on air emissions. The U.S. EPA has noted that, "because of their relatively high efficiency and reliance on natural gas as the primary fuel, gas turbines emit substantially less carbon dioxide (CO2) per kilowatt-hour (kWh) generated than any other fossil technology in general commercial use."

The electric utility sector in the Northeast has achieved major reductions in several air emission areas over the last 20 years-in great part thanks to new, more efficient power sources, from natural gas to renewables.

For example, in New York State over the last 20 years, NY ISO reports that emissions rates from the power sector dropped by 51% for CO2, 89% for NOx, and 98% for SO2. ISO-NE reports that from 2001 to 2018, total emissions from power plants in New England dropped by 98% for sulfur dioxide (SO2), 74% for nitrogen oxides (NOx), and 36% for CO2. PJM emissions data indicates a significant drop in SO2, NOx and CO2 for its entire region, which includes declining trends for all three pollutants in both New Jersey and Pennsylvania.

The chart below shows changes in carbon emissions by the electric power industry in the region, for the years 1990, 2000 and 2019, as an example of the progress that has been made in the region in reducing emissions.

Comparison of Air Pollution
from Fossil Fuels

(average emission rates measured in pounds for air pollutants produced per megawatt hour of electricity generated, U.S.)

  SO2 NOx CO2
Natural Gas 0.1 1.7 1,135
Oil 12 4 1,672
Coal 13 6 2,249
Source: U.S. EPA

Compressed natural gas (CNG) vehicles provide environmental benefits, reliability, cost-effectiveness, and are sourced from domestic supplies. ACEEE rated the CNG vehicle as one of the top 10 "greenest vehicles" on the road. And in October 2009, the National Research Council, affiliated with the National Academies of Science, released a report which observed that "compressed natural gas had lower damages than other options, as the technology's operation and fuel produce very few emissions."

MIT's natural gas study of June 2011 stated that using very efficient natural gas powerplants to replace coal-fired plants is "the most cost-effective way of reducing CO2 emissions in the power sector" over the next 25 to 30 years. Natural gas will also play "a central role in integrating more intermittent renewable sources - wind and solar - into the electricity system because they can easily be brought in and out of service as needed."
Continued investments in gas power generation will yield greater efficiencies and help the region meet its Clean Air-and energy-requirements.

Natural Gas Vehicles (NGVs)

The natural gas vehicle (NGV), also known as CNG vehicles (for compressed natural gas), has many environmental advantages. NGVs remain a very competitive alternative to gasoline or diesel fuels, particularly for certain key markets such as fleets and urban bus systems.
The U.S. Department of Energy's alternative fuel vehicle website notes: "Commercially available medium- and heavy-duty natural gas engines have demonstrated over 90% reductions of carbon monoxide (CO) and particulate matter, and more than 50% reduction in nitrogen oxides (NOx) relative to commercial diesel engines."

According to NGV America, typical dedicated NGVs can reduce exhaust emissions of:
  • Carbon monoxide (CO) by 70%
  • Non-methane organic gas (NMOG) by 87%
  • Nitrogen oxides (NOx) by 87%
  • Carbon dioxide (CO2) by 20 to 30% below those of diesel and gasoline vehicles.

In October 2009, the National Research Council, affiliated with the National Academies of Science, released a report which noted that: "compressed natural gas had lower damages than other options, as the technology's operation and fuel produce very few emissions."

Reducing Methane Emissions within Gas System Operations

The natural gas industry is cognizant of its responsibility to reduce emissions from its system operations.

Many of NGA's distribution and transmission company members already participate in the U.S. EPA's "Natural Gas STAR" Program - progress continues on this front. For 2018 in the U.S., Natural Gas STAR partners reported methane emissions reduction of 130.6 Bcf, providing "cross-cutting benefits" according to EPA. Cumulative reductions nationally since the year 2004 total 1.6 Tcf.

Methane emissions related to U.S. natural gas systems have declined by 23.7% since 1990, according to the EPA's 2018 national GHG inventory report released in April 2020. The report notes: "Overall, natural gas systems emitted 140.0 MMT CO2Eq. (5,598 kt CH4) of CH4 in 2018, a 24 percent decrease compared to 1990 emissions, and less than 1 percent increase compared to 2017 emissions (see Table 3-57and Table 3-58)... Distribution system emissions, which account for 8 percent of CH4 emissions from natural gas systems and less than 1 percent of CO2 emissions, result [sic] mainly from leak emissions from pipelines and stations. An increased use of plastic piping, which has lower emissions than other pipe materials, has reduced both CH4 and CO2 emissions from this stage, as have station upgrades at metering and regulating (M&R) stations. Distribution system CH4 emissions in 2018 were 73 percent lower than 1990 levels and less than 1 percent lower than 2017 emissions. Distribution system CO2 emissions in 2018 were 73 percent lower than 1990 levels and less than 1 percent lower than 2017 emissions." [EPA, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2018, pages ES-16 and Ch. 3, pages 84-86]

For the distribution sector, as indicated above, the main emphasis has been on accelerating the replacement of older, more "leak-prone" pipe. EPA's 2018 GHG report indicates that methane emissions related to the nation's gas distribution system has declined by 73% since 1990 - reflecting tremendous progress in that sector.

As noted above, accelerated pipeline replacement of "leak-prone" system components, such as cast iron, is an industry and U.S. DOT priority - see separate issue brief at:

Shale Gas Production and the Environment

Finally, an environmental issue of interest concerns the development of shale gas resources in the U.S. The MIT study on natural gas from June 2011 notes that "the environmental impacts of shale development are challenging but manageable." Industry and government regulatory agencies are working to address development in an environmentally safe manner.

In August 2011, an advisory group to the U.S. Energy Secretary released a series of consensus-based recommendations calling for increased measurement, public disclosure and a commitment to continuous improvement in the development and environmental management of shale gas. Increased transparency and a focus on best practices "benefits all parties in shale gas production: regulators will have more complete and accurate information, industry will achieve more efficient operations and the public will see continuous, measurable, improvement in shale gas activities," the report says. The report calls for industry leadership in improving environmental performance, underpinned by strong regulations and rigorous enforcement, evolving to meet the identified challenges. Further information can be found here:

The natural gas production industry has moved to address the issue of disclosure regarding the additives used in the hydraulic fracturing process. One major step was announced in 2011, when the Ground Water Protection Council (GWPC) and the Interstate Oil and Gas Compact Commission (IOGCC), with funding support from the United States Department of Energy (DOE), unveiled a landmark web-based national registry disclosing the chemical additives used in the hydraulic fracturing process on a well-by-well basis. The initiative provides energy companies involved in oil and gas exploration and production a single-source means to publically disclose the chemical additives used in the hydraulic fracturing process. The web site address is:

In June 2015, the Environmental Protection Agency (EPA) released a draft assessment on the potential impacts of hydraulic fracturing activities on drinking water resources in the United States. It found potential risks but no major impacts to date. EPA's review of data sources available to the agency found specific instances where well integrity and waste water management related to hydraulic fracturing activities impacted drinking water resources, but they were small compared to the large number of hydraulically fractured wells across the country. In December 2016, EPA released the final study. It is not conclusive on the extent of impacts but cited some potential impacts - which industry would note is often related to improper casing and handling of surface water. The study concludes that "hydraulic fracturing for oil and gas is a practice that continues to evolve." The study notes that by focusing attention of the situations described in the analysis, "impacts on drinking water resources from activities in the hydraulic fracturing water cycle could be prevented or reduced." The study can be found here:

The Pennsylvania Department of Environmental Protection (DEP) in its 2017 Oil and Gas Annual Report released in August 2018, notes that: "Although there is no evidence that hydraulic fracturing has resulted in a direct impact to a water supply in Pennsylvania, there are cases where related oil and gas activities have adversely affected private water supplies. DEP investigates all stray gas-related complaints and if it is determined that a water supply is adversely affected by oil and gas activities, DEP works with the responsible operator to ensure the water supply is restored or replaced."
The Pennsylvania Department of Environmental Protection (DEP) has comprehensive information on its regulatory role regarding shale gas production in that state; it can be found here:

DEP released a number of other relevant studies in 2018 related to natural gas production and the environment.

In April 2018, PA DEP released the first four years of data on well structural soundness submitted by thousands of Pennsylvania oil and gas well operators. A comprehensive analysis of the first year, 2014, shows that the majority of wells in the state are being operated in a manner that greatly reduces the risk for groundwater impacts. The analysis "showed that less than 1 percent of operator observations indicated the types of integrity problems, such as gas outside surface casing, that could allow gas to move beyond the well footprint. The movement of gas or other fluids beyond a well footprint has the greatest potential to result in environmental concerns."

In July 2018, the DEP released a study on natural gas drilling and air emissions. The key findings of the study are that pollutants did not exceed regulatory standards. For example, "The primary criteria pollutant monitoring site, Meddings Road, did not report NAAQS-related values for any of the monitored criteria pollutants (e.g., Ozone, NO2, PM2.5, CO) which exceeded the applicable NAAQS or indicated a probable future exceedance based on the data pattern. In addition, the pattern of recorded pollutant concentration measurements did not indicate a localized source impact which would cause an exceedance of any of the NAAQS evaluated." The DEP also noted that "as unconventional natural gas extraction, gathering, and processing infrastructure develops to maturity, monitoring of criteria pollutants in the project area should continue."

Other issues, such as reducing the use of diesel fuel in the production process, enhancing "green completion" in the entire production cycle to reduce emissions, and mitigating community impacts, continue to receive industry attention, in Pennsylvania and elsewhere. The industry must be responsible for best practices at all times.

For Further Information

U.S. EPA Natural Gas STAR Program

U.S. Alt Fuels Vehicle Center, Natural Gas Vehicle Emissions

U.S. EPA, Greenhouse Gas Emissions

Pennsylvania DEP 2019 Annual Oil & Gas Report, released 2020

Pennsylvania Dept. of Environmental Protection, Marcellus Shale page