Meghan Hodges
The Clean Air Act, passed in 1970, seeks to reduce air pollution in the United States by requiring engines and fuels to produce fewer emissions. Since then, the US Environmental Protection Agency (EPA) has implemented various measures to reduce pollution from gasoline use, including the banning of leaded gasoline and the requirement for cleaner-burning reformulated gasoline. Today, there are several types of gas engines that aim to reduce pollution, such as natural gas vehicles (NGVs) and engines that run on compressed natural gas (CNG) or liquefied natural gas (LNG). Electric vehicles (EVs) have gained popularity due to their lack of tailpipe emissions, although they do produce some emissions during the production and distribution of electricity. Overall, the type of gas engine that creates the least pollution is a topic of ongoing research and development, with various options available that aim to reduce environmental impact.
| Characteristics | Values |
|---|---|
| Engines and fuels that produce less air pollution | Required by the Clean Air Act |
| Emission-control devices | Required on passenger vehicles since 1976 |
| Leaded gasoline | Banned for vehicles |
| Reformulated gasoline | Required cleaner-burning since 1995 |
| Ultra-low sulfur gasoline | Required since 2017 |
| Natural gas vehicles (NGVs) | Meet stringent emissions standards with less complicated emissions controls |
| RNG production methods | Show less GHG emissions and fossil fuel consumption than conventional fossil natural gas and gasoline |
| CNG and LNG | Clean-burning fuels that perform well against current vehicle emissions standards |
| Diesel engines | Emit less carbon dioxide than gasoline engines |
| Electric vehicles (EVs) | No tailpipe emissions |
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What You'll Learn
Natural gas vehicles (NGVs) emit less
NGVs emit very low levels of carbon monoxide (approximately 70% lower than comparable gasoline-powered vehicles) and volatile organic compounds. They also have a considerable effect on breaking down methane and other greenhouse gases in the atmosphere, increasing the global rate of methane decomposition. Dedicated NGVs produce little to no evaporative emissions during fueling and use, while for gasoline vehicles, evaporative and fueling emissions account for at least 50% of a vehicle's total hydrocarbon emissions.
NGVs with ultra-low NOx engines can produce near-zero NOx emissions, meeting the California Air Resources Board's optional near-zero emission standard of 0.02 NOx. CNG, in particular, emits 20-29% less CO2 than diesel and gasoline, with lower carbon and particulate emissions per equivalent distance traveled. Additionally, CNG production uses less petroleum and emits slightly fewer GHGs than LNG because compressing natural gas requires less energy than liquefying it.
The use of NGVs has seen widespread adoption globally, with countries like Pakistan, Argentina, Iran, and Brazil having a large number of NGVs on the road. As of 2015, Iran had the world's largest fleet of NGVs with 3.5 million vehicles, while India had 3.045 million NGVs as of 2010. The growth of the NGV market in these countries can be attributed to governmental interventions to reduce dependence on imported gasoline and to decrease the societal impact of sanctions.
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Diesel engines emit less CO2
Diesel engines are more efficient than gasoline engines, and newer models emit fewer pollutants. However, diesel engines emit higher levels of nitrogen oxides, which have led to decreased sales in Europe and proposed bans in cities like Paris.
Diesel engines, like other internal combustion engines, convert chemical energy from fuel into mechanical power. During ideal combustion, diesel fuel, a hydrocarbon mixture, would only produce carbon dioxide (CO2) and water vapour (H2O). However, in reality, the exhaust gases from diesel engines contain other pollutants, such as unburned hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx), and particulate matter (PM). These pollutants arise from non-ideal combustion processes, such as incomplete fuel combustion and high-temperature reactions.
While diesel engines produce CO2, they generally emit lower levels compared to gasoline engines. This contributes to their reputation for being more environmentally friendly in terms of greenhouse gas emissions. However, it's important to note that diesel engines have been associated with higher emissions of nitrogen oxides (NOx), which can have adverse health and environmental effects.
To address the pollution caused by gasoline use, regulatory bodies like the U.S. Environmental Protection Agency (EPA) have implemented measures such as requiring emissions-control devices and cleaner-burning engines and the elimination of leaded gasoline. Additionally, the Clean Air Act Amendments have played a significant role in reducing air pollution by mandating reformulated gasoline with reduced sulphur content and lower emissions in metropolitan areas.
Natural gas vehicles (NGVs) have emerged as a cleaner alternative, meeting stringent emissions standards with less complicated emissions controls. Argonne National Laboratory's findings highlight the significant reduction in GHG emissions and fossil fuel consumption achieved by compressed natural gas (CNG) and liquefied natural gas (LNG) compared to conventional fossil natural gas and gasoline.
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Electric vehicles (EVs) emit less
While it is true that manufacturing an EV emits more CO2 than manufacturing a similar gasoline-powered vehicle, this is offset by the lower emissions from fuel consumption by EVs. It takes between one and two years of typical driving for an EV to compensate for its higher initial emissions. This payback time will decrease as the electrical grid and battery manufacturing processes become more environmentally friendly.
In geographic areas that use relatively low-polluting energy sources for electricity generation, EVs have a significant life cycle emissions advantage over similar conventional vehicles running on gasoline or diesel. Even in areas with higher-emissions electricity, EVs may still demonstrate a life cycle emissions benefit. As renewable energy sources become more prevalent, the total greenhouse gas emissions associated with EVs are expected to decrease.
The U.S. government is also supporting the transition to EVs by investing up to $7.5 billion to build a national network of electric vehicle chargers. This will increase access to EV charging and make it more convenient for people to adopt EVs.
In conclusion, EVs emit less than gasoline-powered cars, and their carbon footprint is expected to decrease further in the future.
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Ultra-low sulfur gasoline reduces emissions
The Clean Air Act, passed in 1970, seeks to reduce air pollution in the United States. To meet the goals of the Act, the US Environmental Protection Agency (EPA) has implemented several actions, including requiring emissions-control devices and cleaner-burning engines.
One significant development in reducing emissions has been the introduction of ultra-low sulfur gasoline. As of 2017, refiners are mandated to supply gasoline with 97% less sulfur content than in 2004. Gasoline with lower sulfur content is essential for advanced vehicle emission-control devices to function effectively, and it helps to reduce emissions from both old and new vehicles.
The benefits of ultra-low sulfur gasoline are significant. Lower sulfur content enables the use of advanced emissions control technologies, which substantially reduce harmful emissions from fuel combustion. This includes reducing the exhaust output of ozone precursors and particulate matter to near-zero levels.
In addition to ultra-low sulfur gasoline, the EPA has also mandated the use of cleaner-burning reformulated gasoline since 1995 to reduce air pollution in metropolitan areas with high levels of ground-level ozone pollution. Methyl tertiary butyl ether (MTBE) was initially used as an additive to help gasoline burn cleaner, but it was phased out in the late 1990s due to its toxicity and replaced with ethanol.
Another alternative fuel that reduces emissions is natural gas. Compressed natural gas (CNG) and liquefied natural gas (LNG) are clean-burning fuels that meet current vehicle emissions standards. Converting conventional vehicles to operate on natural gas can provide emissions benefits, especially when replacing older models. Renewable natural gas (RNG), or biomethane, yields significantly fewer GHG emissions than conventional fossil natural gas, making it an attractive option for reducing emissions.
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Cleaner-burning reformulated gasoline
The Clean Air Act (first passed in 1970) and its amendments require engines and fuels to produce less air pollution. To meet the air pollution reduction goals of the Act, the US Environmental Protection Agency (EPA) has taken several actions, including requiring emissions-control devices and cleaner-burning engines.
One such action is the introduction of cleaner-burning reformulated gasoline. In 1995, the Clean Air Act Amendments required the use of cleaner-burning reformulated gasoline to reduce air pollution in metropolitan areas with significant ground-level ozone pollution. This gasoline is blended to burn more cleanly than conventional gasoline and reduce emissions of smog-forming and toxic pollutants.
Cleaner-burning gasoline enables catalytic converters to work more effectively, further reducing tailpipe emissions. It has about half the benzene content of earlier gasoline, reducing cancer risks. It also has reduced levels of aromatic hydrocarbons and olefins, which react with other pollutants to form smog. Additionally, it has a lower vapor pressure, ensuring the gasoline evaporates less readily, and reduced distillation temperatures, ensuring more complete combustion.
California, which has the cleanest gasoline in the world, has been at the forefront of implementing cleaner-burning gasoline regulations. Since 1996, all gasoline sold in California for use in motor vehicles must meet specific requirements, reducing smog-forming emissions from motor vehicles by 15% and cancer risk from exposure to motor vehicle toxics by about 40%. The use of cleaner-burning gasoline has contributed to a significant decrease in vehicle emissions and improved air quality in the state.
Other states, such as Arizona, have also adopted the use of cleaner-burning gasoline in certain areas due to air quality regulations. The EPA continues to work towards reducing pollution from gasoline use, with recent actions including requiring ultra-low sulfur gasoline and supporting research on alternative, lead-free fuels for piston-engine aircraft.
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Frequently asked questions
Natural gas engines create less pollution than conventional fossil fuel engines. Compressed natural gas (CNG) and liquefied natural gas (LNG) are clean-burning fuels that perform well against current vehicle emissions standards.
Tailpipe emissions are the result of fuel combustion in a vehicle's engine. The primary emissions of concern include hydrocarbons, oxides of nitrogen (NOx), carbon monoxide (CO), and carbon dioxide (CO2).
Natural gas vehicles (NGVs) can meet stringent emissions standards with less complicated emissions controls. NGVs with ultra-low NOx engines can produce near-zero NOx emissions.
CNG production uses less petroleum and emits slightly fewer greenhouse gas emissions (GHG) than LNG because compressing natural gas requires less energy than liquefying it.
Three techniques used to meet emission regulations include in-cylinder purification, exhaust gas after-treatment, and fuel technologies. Biodiesel is also being used to address environmental issues and meet regulations.
