Helena Joyce
Gasoline is a major source of air pollution, with harmful gases and compounds being released into the atmosphere through vehicle emissions, leaks, and evaporation. The pollutants emitted from gasoline combustion fall into two categories: criteria and non-criteria pollutants. Criteria pollutants are regulated by the Clean Air Act (CAA) and include carbon monoxide (CO), nitrogen oxides (NOx), and volatile organic compounds (VOCs). Non-criteria pollutants, such as formaldehyde, benzene, and fluorinated refrigerants, are not regulated despite their harmful effects on health and air quality. To reduce pollution, some states have implemented measures such as setting limits on tailpipe emissions, requiring new vehicle technology, and controlling fuel composition. Additionally, the removal of toxic chemicals like methyl tertiary butyl ether (MTBE) from gasoline has been a focus of pollution reduction efforts.
| Characteristics | Values |
|---|---|
| Pollutant removed from gasoline | Methyl tertiary butyl ether (MTBE) |
| Replacement | Ethanol |
| Year of phase-out | By 2007 |
| Pollutants emitted from gasoline | Carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbon (HFC), benzene, 1,3-Butadiene, formaldehyde, carbon monoxide (CO), nitrogen oxides (NOx), ozone, fluorinated refrigerants, water vapour |
| Health and environmental effects | Benzene is a known human carcinogen that increases the incidence of leukemia and causes blood disorders in humans. Formaldehyde is a probable human carcinogen with links to lung and airway cancer. 1,3-Butadiene is classified as a probable human carcinogen and is correlated with cardiovascular disease. Carbon monoxide can exacerbate cardiovascular disease and damage the central nervous system. Nitrogen oxides contribute to acid rain, climate change, deteriorated water quality, ground-level ozone, air toxics, and particulate matter. Ozone is a powerful oxidant that can reduce lung function, aggravate asthma, increase the risk of respiratory illness, and lead to permanent lung damage. |
| Exposure to gasoline | Breathing vapors when filling a car's fuel tank, contaminated soil or water, leaks or spills from underground storage tanks or pipelines, evaporation from untreated water |
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What You'll Learn
Benzene, toluene, ethylbenzene, and xylene (BTEX)
The Canadian Environmental Protection Act, 1999, includes Federal Environmental Quality Guidelines (FEQGs) for BTEX. These guidelines describe the acceptable quality of the ambient environment and are based on the toxicological effects or hazards of specific substances or groups of substances. FEQGs can help prevent pollution by providing targets for acceptable environmental quality and can also be used to evaluate the significance of concentrations of chemical substances currently found in the environment, such as in water, sediment, soil, and biological tissue.
BTEX compounds have various industrial applications. Toluene is used in the synthesis of chemicals, including benzene and toluene diisocyanate. It is also used as a solvent in adhesives, fingernail polish, lacquers, leather tanning, paint thinners, paints, printing, and rubber. Ethylbenzene is primarily used in the production of styrene and polystyrene foam, as well as a solvent in consumer products like adhesives, coatings dyes, perfumes, pharmaceuticals, plastics, rubber, and varnishes. Xylene is another solvent used in cleaning agents, paint thinners, and varnishes.
While gasoline itself contributes to environmental issues and pollution, it is important to note that the burning of gasoline without ethanol produces about 19 pounds of carbon dioxide (CO2) per gallon burned. The use of ethanol in gasoline helps to reduce these CO2 emissions, as ethanol has less carbon per gallon.
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MTBE replaced by ethanol
Gasoline is a mixture of gasoline and up to 10% ethanol, often referred to as E10. The formulation varies depending on the season, region, and other factors. While vehicles that use ethanol blends have slightly lower fuel economy, their carbon dioxide (CO2) tailpipe emissions per mile are similar to those of vehicles that use gasoline without ethanol. This is because ethanol has less carbon per gallon than gasoline.
Methyl tertiary butyl ether (MTBE) is a chemical compound manufactured by the chemical reaction of methanol and isobutylene. It is a volatile, flammable, and colorless liquid that dissolves easily in water. MTBE is almost exclusively used as a fuel additive in motor gasoline to help it burn cleaner.
In 1995, high levels of MTBE were discovered in the water wells of Santa Monica, California. Subsequent findings indicated that tens of thousands of water wells across the country were contaminated. MTBE spreads more easily underground than other gasoline components due to its higher solubility in water. It also imparts an unpleasant taste to water, even at low concentrations.
Due to the contamination concerns, the use of MTBE in gasoline was banned in several U.S. states beginning in the late 1990s. By 2007, the U.S. refining industry had voluntarily stopped using MTBE in reformulated gasoline. MTBE was replaced by ethanol, which is not toxic and does not pose the same groundwater contamination risks.
The federal Energy Policy Act of 2005 removed the oxygenate requirement for reformulated gasoline and established a renewable fuel standard. This, along with the lack of MTBE liability protection in the law, prompted refiners to switch from MTBE to ethanol.
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Carbon dioxide (CO2) emissions
Carbon dioxide (CO2) is a greenhouse gas and a product of burning gasoline. It is the most abundant greenhouse gas in the transportation sector. In 2022, CO2 emissions from aviation and motor gasoline combustion in the US were about 1,067 million metric tons, or 22% of total US energy-related CO2 emissions.
A typical passenger vehicle emits about 4.6 metric tons of CO2 per year. This assumes an average fuel economy of 22.2 miles per gallon and 11,500 miles driven per year. Every gallon of gasoline burned creates about 8,887 grams of CO2, or about 20 pounds. The average passenger vehicle emits about 400 grams of CO2 per mile.
The amount of CO2 emitted from burning gasoline varies depending on the ethanol content of the fuel. Gasoline sold in the US typically contains up to 10% ethanol, known as E10. Ethanol has less carbon per gallon than gasoline, so the CO2 emissions per mile are similar to that of pure gasoline, despite a slightly lower fuel economy.
In addition to CO2, automobiles using gasoline produce methane (CH4) and nitrous oxide (N2O) from the tailpipe. Gasoline leaks from pipelines, storage tanks, and fuel leaks from vehicles also contribute to environmental pollution. To reduce air pollution, the Clean Air Act requires engines and fuels to produce less air pollution.
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Nitrogen oxides (NOx)
NOx emissions are a significant environmental concern, with approximately 55% of human-made NOx emissions originating from motor vehicles. The high-temperature combustion of gasoline in car engines is a major source of NOx, especially in areas with high traffic congestion, such as large cities. The Clean Air Act (CAA) aims to reduce air pollution by setting standards for common pollutants, including NOx, through regulations enforced by the U.S. Environmental Protection Agency (EPA).
NOx emissions contribute to a range of environmental issues beyond air pollution. They play a role in climate change, water quality deterioration, ground-level ozone depletion, air toxics, and particulate matter. NOx is also produced naturally by lightning, and the oxidation of NOx from lightning can result in the formation of nitric acid, which contributes to acid rain.
Additionally, agricultural practices, such as the use of nitrogen fertilizers and nitrogen-fixing plants, contribute significantly to atmospheric NOx levels. The nitrification process, which involves transforming ammonia into nitrate, releases NOx into the atmosphere. This has led to changes in forest compositions and increased NOx levels in certain regions.
While gasoline combustion is a significant contributor to NOx emissions, it is important to note that the addition of ethanol to gasoline blends can help reduce CO2 emissions per mile, as ethanol contains less carbon per gallon. Electric vehicles (EVs) and fuel cell electric vehicles (FCEVs) offer further environmental benefits by eliminating tailpipe emissions associated with gasoline-powered engines.
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Air toxics and particulate matter (PM)
Particulate matter (PM) refers to a mixture of solid particles and liquid droplets found in the air. Some particulate matter is large enough to be seen, such as dust, dirt, soot, or smoke, while other particles are so small they can only be detected using an electron microscope. PM can be emitted directly from sources such as construction sites, unpaved roads, fields, smokestacks, or fires, but most particles form in the atmosphere as a result of complex reactions of chemicals. PM is commonly divided into PM10 and PM2.5, referring to particles with a diameter of 10 micrometers or less, and fine particles with a diameter of 2.5 micrometers or less, respectively. PM2.5 is a component of PM10 and poses the greatest risk to health, as these particles can be inhaled deep into the lungs and may even enter the bloodstream. Short-term exposure to PM10 has been linked to the worsening of respiratory diseases, while long-term exposure to PM2.5 has been associated with premature death, particularly in those with chronic heart or lung diseases, and reduced lung function growth in children.
In addition to the health impacts, PM, primarily PM2.5, reduces visibility by altering the way light is absorbed and scattered in the atmosphere. This contributes to haze, affecting the appearance of national parks and wilderness areas. Furthermore, some constituents of PM promote climate warming, while others have a cooling influence, so ambient PM has both warming and cooling properties. PM can also aggravate asthma, emphysema, bronchitis, heart disease, and lung disease, and it is a carrier of many toxic compounds. It contributes to the pollution of fresh and coastal waters and the contamination of farmland and natural ecosystems.
To address the issues associated with air toxics and particulate matter, the Clean Air Act (CAA) requires the U.S. Environmental Protection Agency (EPA) to set standards for common pollutants, including PM2.5. The EPA also provides air quality alerts through the Air Quality Index (AQI), which helps individuals understand when to take action to protect their health. Additionally, the use of ethanol as a replacement for toxic chemicals in gasoline has helped to reduce air pollution.
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Frequently asked questions
Pollutants that are removed from gasoline include methyl tertiary butyl ether (MTBE), lead, benzene, formaldehyde, and carbon dioxide (CO2).
Methyl tertiary butyl ether (MTBE) is a chemical previously added to gasoline to help it burn cleaner. However, due to its toxicity, it has been replaced with ethanol in the United States since 2007.
Removing pollutants from gasoline is crucial to reduce air pollution and mitigate potential adverse health effects and environmental damage. Pollutants in gasoline emissions have been linked to climate change, respiratory issues, and increased cancer risk.
Pollutants can enter the environment through gasoline leaks, spills, improper disposal, and vehicle emissions. Leaks can occur during the filling of gas tanks at gas stations, from open gas tanks, or in pipelines and underground storage tanks.
Pollutants in gasoline, such as benzene and formaldehyde, are known or probable human carcinogens. They have been associated with an increased risk of leukemia, lung and airway cancer, and adverse effects on fetal development. Additionally, pollutants like carbon monoxide (CO) can exacerbate cardiovascular disease and, at high levels, can be poisonous and cause central nervous system damage.
