Natural Gas & Environment

Natural Gas & Environment

V.A. Raju & Dr. A.N. Giri

The preservation of our environment is a very important and pressing topic, particularly when dealing with energy issues. The advancement of technology, particularly technologies that allow the cleaner use of fossil fuels, may provide many environmental benefits and allow us to use cleaner energy. Natural gas is the cleanest of the fossil fuels, and thus its many applications can serve to decrease harmful pollution levels from all sectors, particularly when used together with or replacing other fossil fuels. The natural gas industry itself is also committed to ensuring that the process of producing natural gas is as environmentally-friendly as possible. 

This section focuses on sulfur compounds in natural gas, Origin and history of NG, Description and Technical Characteristics, Quality & the environmental issues related to the use of natural gas, as well as the advancement of new and exciting technologies within the industry.

ISO 6326-1:2007 gives a brief description of standardized methods that can be used for the determination of sulfur compounds in natural gas. The principle of each method is described generally, the range of concentrations for which the method is suitable It should enable the user to select judiciously the proper method for the application being considered. Sulfur analysis is performed in order to determine total sulfur, sulfur contained in specific groups [e.g. thiols (mercaptans)], individual sulfur compounds and specific groups of sulfur compounds.

The available standardized methods in the field of sulfur analysis are the Wickbold combustion method for total sulfur determination (ISO 4260); the Lingener combustion method for total sulfur determination (ISO 6326-5); gas chromatography for determination of individual sulfur compounds (ISO 19739); potentiometry for determination of hydrogen sulfide, carbonyl sulfide and thiol compounds (ISO 6326-3).

Sulfur compounds can occur naturally in natural gas and remain as traces after treatment, or they may have been injected deliberately to allow subsequent olfactory detection for safety reasons.

The standardization of several methods for the determination of sulfur compounds in natural gas is necessary in view of the diversity of these compounds [hydrogen sulfide, carbonyl sulfide, tetrahydrothiophene (THT), etc.] and the requirements of the determinations (required uncertainty, measurement at the well head, at clean-up plant or in the transmission pipes, etc.).

Tetrahydrothiophene is a heterocyclic organic compound consisting of a five-membered ring containing four carbon atoms and a sulfur atom. It is the saturated analog of thiophene. It is a volatile, clear, colorless liquid with a strong unpleasant odor.

Because of its smell, tetrahydrothiophene is occasionally used as an odorant in natural gas, in place of the more common ethanethiol. It is also used as a solvent, as an insecticide, and as a moth repellent. It is an intermediate in the preparation of the solvent sulfolane, which is produced by the oxidation of tetrahydrothiophene. It is also used as an electrolyte for lithium batteries.

As an odorant, it has numerous advantages against ethanethiol. It is not corrosive to the gas pipes and valves, it does not cause habitual deactivation of sense of smell, and it does not cause irritant responses of coughing, tears, and headache. It is regarded to be an ideal gas indicator in use

The other parts of ISO 6326 and ISO 19739 describe in detail the various standardized methods.

Gas Chromatograph

The gas chromatograph determines the gas composition. The gas components are defined: Methane C₁ Ethane C₂ Propane C₃ Iso-butane i−C₄ Normal butane n−C₄ Iso-pentane i−C₅ Normal pentane n−C₅ Hexane and heavier hydrocarbons C₆+ Nitrogen N₂ Carbon dioxide CO₂ In each analysis, the gas chromatograph performs the following calculations, in accordance with ISO 6976 ,Gross Calorific Value at reference conditions, Relative density ,Wobbe index 

Density at reference conditions

The chromatograph periodically carries out a calibration gas analysis, either, automatically or manually. The response factors for each component are tested between two successive calibration analyses. Variations of these should be within limits specified by international standard ISO 6974.

Gas Chromatograph Calibration This procedure includes:

Response factors check resulting from consecutive analysis of the calibration gas based on the international standard ISO 6974 .Concentrations check resulting from consecutive analysis of the standard gas

calculation check of Gross Calorific Value of natural gas from the chromatograph based on the international standard ISO 6976 and check of the certified composition of standard gas on chromatograph.

Superior calorific value:

The amount of heat which would be released by the complete combustion in air of a specified quantity of gas, in such a way that the pressure p1 at which the reaction takes place remains constant, and all the products of combustion are returned to the same specified temperature t1 as that of the reactants, all of these products being in the gaseous state except for water formed by combustion, which is condensed to the liquid state at t1.

A synonym for calorific value is the term heating value. Calorific values can be specified on a molar or mass basis. Then the calorific value depends on the combustion reference conditions t1 and p1. More commonly, calorific values are determined based upon a volumetric basis ;in this instance, the calorific value needs to be specified with the combustion reference conditions t1 and p1 as well as the volumetric reference conditions t2 and p2.

Wobbe index:

The superior calorific value on a volumetric basis at specified reference conditions, divided by the square root of the relative density at the same specified metering reference conditions.

The Wobbe index is an important quality designation for natural gas, which is commonly used to determine trade prices and the interchangeability of natural gas.

Origin and history of NG

The discovery of natural gas dates from ancient times in the Middle East. Thousands of years ago, it was noticed that natural gas seeps ignited when lightning and created "burning springs". In Persia, Greece or India, people built temples around these "eternal flames" for their religious practices. However they did not recognize the energy value of natural gas. It was done in China around 900 BC. The Chinese drilled the first known natural gas well in 211 BC.

In Europe, natural gas was unknown until it was discovered in Great Britain in 1659 although it was not commercialized until about 1790. In 1821 in Fredonia, United States, residents observed gas bubbles rising to the surface from a creek. William Hart, considered as America's "father of natural gas", dug there the first natural gas well in North America.

Throughout the 19th century, natural gas was used almost exclusively as source of light and its use remained localized because of lack of transport structures, making difficult to transport large quantities of natural gas through long distances. There was an important change in 1890 with the invention of leak proof pipeline coupling. However, existing techniques did not allow for gas going further than 160 km. and it was mostly flared of left in the earth. Transportation of natural gas to long distances became practical in the 1920s as a result of technological advances in pipelines. It was only after World War II that the use of natural gas grew rapidly because of the development of pipeline networks and storage systems.

In the early days of oil exploration, natural gas was often an unwelcome by-product, as natural gas reservoirs were tapped in the drilling process and workers were forced to stop drilling to let the gas vent freely into the air. Now, and particularly after the oil shortages of the seventies, natural gas has become an important source of energy in the world.

The gas industry has been highly regulated for many years mainly as it was regarded as a natural monopoly. In the last 30 years there has been a move away from price regulation and towards liberalization of natural gas markets. These movements have resulted in greater competition in the market and in a dynamic and innovative natural gas industry. In addition, thanks to technological advances natural gas can be better explored, extracted and transported to consumers. Innovations also help to improve natural gas applications and create new ones. Natural gas is increasingly used for power generation.

Natural gas is a fossil fuel source of energy, which represents more than one fifth of total energy consumption in the world. It has been the fastest growing fossil fuel since the seventies.

Due to economical and ecological advantages that it presents as well as its safety qualities (e.g. reduced flammable range), natural gas is an increasingly attractive source of energy in many countries. At present, natural gas is the second energy source after oil. According to Energy Information Administration, natural gas accounted for 23% of world energy production in 1999. It has excellent perspectives for future demand. Natural gas is considered the fossil fuel of this century, as petroleum was last century and coal two centuries ago.

Total primary energy supply by fuel

Source: World Energy Outlook 2000, International Energy Agency

Natural gas presents a competitive advantage over other energy sources. It is seen as economically more efficient because only about ten per cent of the natural gas produced is wasted before it gets to final consumption. In addition, technological advances are constantly improving efficiencies in extraction, transportation and storage techniques as well as in equipment that uses natural gas.

Natural gas is considered as an environmentally friendly clean fuel, offering important environmental benefits when compared to other fossil fuels. The superior environmental qualities over coal or oil are that emissions of sulphur dioxide are negligible or that the level of nitrous oxide and carbon dioxide emissions is lower. This helps to reduce problems of acid rain, ozone layer or greenhouse gases.

Natural gas is also a very safe source of energy when transported, stored and used.

Although resources of natural gas are finite and natural gas is a non-renewable source of energy, these resources are plentiful all over the world. Natural gas reserves are continuously increasing as new exploration and extraction techniques allow for wider and deeper drilling.

The growing importance of natural gas as a major energy source is shown by the amount of investment devoted to the natural gas industry. The sector shows a great dynamism at the beginning of the new millennium. Increasing demand and prices in the recent past have led to new expansion and exploration projects in the natural gas industry. New pipeline construction projects are developed and planned all over the world. Furthermore, most governments are progressively including natural gas in their energy policy agenda, by following liberalization policies (particularly after the energy shortages of 1970s), in order to open the markets to competition. More and more, energy final users are also showing a preference for using natural gas as a clean, safe, reliable and economical source of energy. Natural gas is used for heating, cooling and several other industry uses, while it is increasingly becoming the favoured fuel for power generation.

Description/Technical Characteristics

Natural gas is colourless, odourless, tasteless, shapeless and lighter than air. It is gaseous at any temperature over -161º C. When it is at its natural state, it is not possible to see or smell natural gas. For safety reasons, a chemical odorant that smells a little like rotten eggs, Mercaptan, is added to natural gas so that it can be smelled if there is a gas leak.

Natural gas is a mixture of light hydrocarbons including methane, ethane, propane, butanes and pentanes. Other compounds found in natural gas include CO2, helium, hydrogen sulphide and nitrogen. The composition of natural gas is never constant, however, the primary component of natural gas is methane (typically, at least 90%), which has a simple hydrocarbon structure composed of one carbon atom and four hydrogen atoms (CH4). Methane is highly flammable, burns easily and almost completely, while it emits very little air pollution. Natural gas is neither corrosive nor toxic, its ignition temperature is high, and it has a narrow flammability range, making it an inherently safe fossil fuel compared to other fuel sources. In addition, because of its specific gravity of 0.60, lower than that of air (1.00), natural gas rises if escaping, thus dissipating from the site of any leak.

The carbon and hydrogen in natural gas are thought to have originated from the remains of plants and animals that were accumulated at the bottom of lakes and oceans over millions of years. After having been buried under huge layers of other sediments, the organic material is transformed into crude oil and natural gas as a result of the high pressure from the layers of sediments and the heat from the earth's core. The oil and gas are then squeezed out of the marine shales in which they were deposited, and from there go into porous sedimentary rocks. Oil and gas migrates upward through the porous rock, as it is less dense than the water, which fills the pores. Several different types of oil and gas "traps" exist.

Natural gas is found throughout the world in reservoirs deep beneath the surface of the earth and floor of the oceans. It forms as pockets of gas over crude oil deposits or is trapped in porous rock formations. Natural gas can be found in oil deposits, as associated natural gas, although non-associated natural gas is often found without the presence of oil.

When natural gas is cooled to a temperature of approximately -260°F at atmospheric pressure, it condenses to a liquid called liquefied natural gas (LNG). One volume of this liquid takes up about 1/600th the volume of natural gas. LNG weighs less than one-half that of water, actually about 45% as much. LNG is odourless, colourless, non-corrosive, and non-toxic. When vaporized it burns only in concentrations of 5% to 15% when mixed with air. Neither LNG, nor its vapour, can explode in an unconfined environment. Since LNG takes less volume and weight, natural gas is liquefied for ease of storing and transporting.

Natural gas is considered as a clean fuel because of its environmentally friendly properties: commercialised natural gas is practically sulphur free and thus it produces virtually no sulphur dioxide (SO2), natural gas emits lower levels of nitrogen oxides (NOx) emissions than oil or coal and emissions of carbon dioxide (CO2) are less than those of other fossil fuels (According to Eurogas 40-50% less than coal and 25-30% less than oil).

Quality

Quantities of natural gas are measured in cubic metres (at a pressure of 75,000 Pascal and a temperature of 15º C) or in cubic feet (at the same pressure and temperature). Normally, gas production from wells and supplies to power plants are measured in thousands or millions of cubic feet (Mcf and MMcf); resources and reserves are calculated in trillions of cubic feet (Tcf).

The amount of energy that is obtained from the burning of a volume of natural gas is measured in British thermal units (Btu). The value of natural gas is calculated by its Btu content. One Btu is the quantity of heat required to raise the temperature of one pound of water of 1 degree Fahrenheit at atmospheric pressure. A cubic foot of natural gas on the average gives off 1,000 Btu, but the range of values is between 500 and 1,500 Btu.

Energy content of natural gas is variable and depends on its accumulations which are influenced by the amount and types of energy gases they contain: the more non-combustible gases in a natural gas, the lower the Btu value. In addition, the volumic mass of energy gases which are present in a natural gas accumulation also influences the Btu value of natural gas. The more carbon atoms in a hydrocarbon gas, the higher its Btu value.

Btu analyses of natural gas are done at each stage of the supply chain. Gas chromatographic process analysers are used in order to conduct fractional analysis of the natural gas streams, separating natural gas into identifiable components. The components and their concentrations are converted into a gross heating value in Btu-cubic foot.

The composition of natural gas varies depending on the field, formation or reservoir from which it is extracted. The different hydrocarbons that form natural gas can be separated using their different physical properties as weight, boiling point or vapour pressure. Depending on its content of heavy components, natural gas can be considered as rich (five or six gallons or more of recoverable hydrocarbons per cubic feet) or lean (less than one gallon of recoverable hydrocarbons per cubic feet).

Normally, natural gas as it is when extracted is not suitable for pipeline transportation or commercial use before being processed. Natural gas for commercial distribution is composed almost entirely of methane and ethane, while moisture and other components have been removed. Pipelines set their specifications for the quality of natural gas. In any case, natural gas must be processed in order to remove unwanted water vapour, solids or other contaminants and to get those hydrocarbons that have a higher value as separate products.

Emissions from the Combustion of Natural Gas

Natural gas is the cleanest of all the fossil fuels, as evidenced in the Environmental Protection Agency’s data comparisons in the chart below, which is still current as of 2010. Composed primarily of methane, the main products of the combustion of natural gas are carbon dioxide and water vapor, the same compounds we exhale when we breathe. Coal and oil are composed of much more complex molecules, with a higher carbon ratio and higher nitrogen and sulfur contents. This means that when combusted, coal and oil release higher levels of harmful emissions, including a higher ratio of carbon emissions, nitrogen oxides (NOx), and sulfur dioxide (SO2). Coal and fuel oil also release ash particles into the environment, substances that do not burn but instead are carried into the atmosphere and contribute to pollution. The combustion of natural gas, on the other hand, releases very small amounts of sulfur dioxide and nitrogen oxides, virtually no ash or particulate matter, and lower levels of carbon dioxide, carbon monoxide, and other reactive hydrocarbons.

Fossil Fuel Emission Levels - Pounds per Billion Btu of Energy Input
Pollutant	Natural Gas	Oil	Coal
Carbon Dioxide	117,000	164,000	208,000
Carbon Monoxide	40	33	208
Nitrogen Oxides	92	448	457
Sulfur Dioxide	1	1,122	2,591
Particulates	7	84	2,744
Mercury	0.000	0.007	0.016
Source: EIA - Natural Gas Issues and Trends 1998

Natural gas, as the cleanest of the fossil fuels, can be used in many ways to help reduce the emissions of pollutants into the atmosphere. Burning natural gas in the place of other fossil fuels emits fewer harmful pollutants, and an increased reliance on natural gas can potentially reduce the emission of many of these most harmful pollutants.

Pollutants emitted in the United States, particularly from the combustion of fossil fuels, have led to the development of many pressing environmental problems. Natural gas, emitting fewer harmful chemicals into the atmosphere than other fossil fuels, can help to mitigate some of these environmental issues. These issues include:

Pollution from the Transportation Sector - Natural Gas Vehicles

Greenhouse Gas Emissions

Global warming, or the 'greenhouse effect' is an environmental issue that deals with the potential for global climate change due to increased levels of atmospheric 'greenhouse gases'. There are certain gases in our atmosphere that serve to regulate the amount of heat that is kept close to the earth's surface. Scientists theorize that an increase in these greenhouse gases will translate into increased temperatures around the globe, which would result in many disastrous environmental effects. In fact, the Intergovernmental Panel on Climate Change (IPCC) predicts in its 'Fourth Assessment Report' released in 2007 that during the 21st century, global average temperatures are expected to rise by between 2.0 and 11.5 degrees Fahrenheit.  A Fifth Assessment Report is expected to be released by the IPCC between 2013 and 2015.

The principle greenhouse gases include water vapor, carbon dioxide, methane, nitrogen oxides, and some engineered chemicals such as chlorofluorocarbons. While most of these gases occur in the atmosphere naturally, levels have been increasing due to the widespread burning of fossil fuels by growing human populations. The reduction of greenhouse gas emissions has become a primary focus of environmental programs in countries around the world.

One of the principle greenhouse gases is carbon dioxide. Although carbon dioxide does not trap heat as effectively as other greenhouse gases (making it a less potent greenhouse gas), the sheer volume of carbon dioxide emissions into the atmosphere is very high, particularly from the burning of fossil fuels. In fact, according to the Energy Information Administration in its December 2009 report 'Emissions of Greenhouse Gases’ in the United States, 81.3 percent of greenhouse gas emissions in the United States in 2008 came from energy-related carbon dioxide.

Because carbon dioxide makes up such a high proportion of U.S. greenhouse gas emissions, reducing carbon dioxide emissions can play a pivotal role in combating the greenhouse effect and global warming. The combustion of natural gas emits almost 30 percent less carbon dioxide than oil, and just under 45 percent less carbon dioxide than coal.

One issue that has arisen with respect to natural gas and the greenhouse effect is the fact that methane, the principle component of natural gas, is itself a potent greenhouse gas. Methane has an ability to trap heat almost 21 times more effectively than carbon dioxide. According to the Energy Information Administration, although methane emissions account for only 1.1 percent of total U.S. greenhouse gas emissions, they account for 8.5 percent of the greenhouse gas emissions based on global warming potential. Sources of methane emissions in the U.S. include the waste management and operations industry, the agricultural industry, as well as leaks and emissions from the oil and gas industry itself. A major study performed by the Environmental Protection Agency (EPA) and the Gas Research Institute (GRI), now Gas Technology Institute, in 1997 sought to discover whether the reduction in carbon dioxide emissions from increased natural gas use would be offset by a possible increased level of methane emissions. The study concluded that the reduction in emissions from increased natural gas use strongly outweighs the detrimental effects of increased methane emissions.  More recently in 2011, researchers at the Carnegie Mellon University released “Life cycle greenhouse gas emissions of Marcellus shale gas”, a report comparing greenhouse gas emissions from the Marcellus Shale region with emissions from coal used for electricity generationIn 1993, the natural gas industry joined with EPA in launching the Natural Gas STAR Program to reduce methane emissions.  The STAR program has chronicled dramatic reductions to methane emissions, since that time:

Smog, Air Quality and Acid Rain

Smog and poor air quality is a pressing environmental problem, particularly for large metropolitan cities. Smog, the primary constituent of which is ground level ozone, is formed by a chemical reaction of carbon monoxide, nitrogen oxides, volatile organic compounds, and heat from sunlight. As well as creating that familiar smoggy haze commonly found surrounding large cities, particularly in the summer time, smog and ground level ozone can contribute to respiratory problems ranging from temporary discomfort to long-lasting, permanent lung damage. Pollutants contributing to smog come from a variety of sources, including vehicle emissions, smokestack emissions, paints, and solvents. Because the reaction to create smog requires heat, smog problems are the worst in the summertime.

The use of natural gas does not contribute significantly to smog formation, as it emits low levels of nitrogen oxides, and virtually no particulate matter. For this reason, it can be used to help combat smog formation in those areas where ground level air quality is poor. The main sources of nitrogen oxides are electric utilities, motor vehicles, and industrial plants. Increased natural gas use in the electric generation sector, a shift to cleaner natural gas vehicles, or increased industrial natural gas use, could all serve to combat smog production, especially in urban centers where it is needed the most. Particularly in the summertime, when natural gas demand is lowest and smog problems are the greatest, industrial plants and electric generators could use natural gas to fuel their operations instead of other, more polluting fossil fuels. This would effectively reduce the emissions of smog causing chemicals, and result in clearer, healthier air around urban centers.

For more information on smog, including the major contributors to smog formation and what is currently being done to combat smog levels, visit the EPA's smog information section.

Particulate emissions also cause the degradation of air quality in the United States. These
particulates can include soot, ash, metals, and other airborne particles. Natural gas emits virtually no particulates into the atmosphere: in fact, emissions of particulates from natural gas combustion are 90 percent lower than from the combustion of oil, and 99 percent lower than burning coal.

Acid rain is another environmental problem that affects much of the Eastern United States, damaging crops, forests, wildlife populations, and causing respiratory and other illnesses in humans. Acid rain is formed when sulfur dioxide and nitrogen oxides react with water vapor and other chemicals in the presence of sunlight to form various acidic compounds in the air. The principle source of acid rain-causing pollutants, sulfur dioxide and nitrogen oxides, are coal fired power plants. Since natural gas emits virtually no sulfur dioxide, and up to 80 percent less nitrogen oxides than the combustion of coal, increased use of natural gas could provide for fewer acid rain causing emissions.

Industrial and Electric Generation Emissions

The use of natural gas to power both industrial boilers and processes and the generation of electricity can significantly improve the emissions profiles for these two sectors.

Natural gas is becoming an increasingly important fuel in the generation of electricity. As well as providing an efficient, competitively priced fuel for the generation of electricity, the increased use of natural gas allows for the improvement in the emissions profile of the electric generation industry. According to the National Environmental Trust (NET), Natural gas-fired electric generation and natural gas-powered industrial applications offer a variety of environmental benefits and environmentally friendly uses, including:

Fewer Emissions - Combustion of natural gas, used in the generation of electricity, industrial boilers, and other applications, emits lower levels of NOx, CO2, and particulate emissions, and virtually no SO2 and mercury emissions. Natural gas can be used in place of, or in addition to, other fossil fuels, including coal, oil, or petroleum coke, which emit significantly higher levels of these pollutants.

Reduced Sludge – Coal-fired power plants and industrial boilers that use scrubbers to reduce SO2 emissions levels generate thousands of tons of harmful sludge. Combustion of natural gas emits extremely low levels of SO2, eliminating the need for scrubbers, and reducing the amounts of sludge associated with power plants and industrial processes.

Reburning - This process involves injecting natural gas into coal or oil fired boilers. The addition of natural gas to the fuel mix can result in NOx emission reductions of 50 to 70 percent, and SO2 emission reductions of 20 to 25 percent.

Cogeneration - The production and use of both heat and electricity can increase the energy efficiency of electric generation systems and industrial boilers, which translates to the combustion of less fuel and the emission of fewer pollutants. Natural gas is the preferred choice for new cogeneration applications.

Combined Cycle Generation – Combined-cycle generation units generate electricity and capture normally wasted heat energy, using it to generate more electricity. Like cogeneration applications, this increases energy efficiency, uses less fuel, and thus produces fewer emissions. Natural gas-fired combined-cycle generation units can be up to 60 percent energy efficient, whereas coal and oil generation units are typically only 30 to 35 percent efficient.

Fuel Cells - Natural gas fuel cell technologies are in development for the generation of electricity. Fuel cells are sophisticated devices that use hydrogen to generate electricity, much like a battery. No emissions are involved in the generation of electricity from fuel cells, and natural gas, being a hydrogen rich source of fuel, can be used. Although still under development, widespread use of fuel cells could in the future significantly reduce the emissions associated with the generation of electricity.

Essentially, electric generation and industrial applications that require energy, particularly for heating, use the combustion of fossil fuels for that energy. Because of its clean burning nature, the use of natural gas wherever possible, either in conjunction with other fossil fuels, or instead of them, can help to reduce the emission of harmful pollutants.

According to the Congressional Research Service’s 2010 report: “Displacing Coal with Generation from Existing Natural-Gas Fired Power Plants,” if natural-gas combined cycle plants utilization were to be doubled from 42 percent capacity factor to 85 percent, then the amount of power generated would displace 19 percent of the CO2 emissions attributed to coal-fired electricity generation.

Pollution from the Transportation Sector - Natural Gas Vehicles

The transportation sector (particularly cars, trucks, and buses) is one of the greatest contributors to air pollution in the United States. Emissions from vehicles contribute to smog, low visibility, and various greenhouse gas emissions. According to the Department of Energy (DOE), about half of all air pollution and more than 80 percent of air pollution in cities are produced by cars and trucks in the United States. Currently, automobile manufacturers are under pressure to produce more environmentally friendly vehicles.

Natural gas can be used in the transportation sector to cut down on these high levels of pollution from gasoline and diesel powered cars, trucks, and buses. According to the EPA, compared to traditional vehicles, vehicles operating on compressed natural gas have reductions in carbon monoxide emissions of 90 to 97 percent, and reductions in carbon dioxide emissions of 25 percent. Nitrogen oxide emissions can be reduced by 35 to 60 percent, and other non-methane hydrocarbon emissions could be reduced by as much as 50 to 75 percent.