United States vehicle emission standards

United States vehicle emission standards are officially determined levels of pollutants that may be legally produced by a vehicle. Most vehicles in the United States and other countries are powered by engines that burn fuel, often gasoline or diesel, to produce the energy needed for locomotion. Although a perfect engine would convert fuel into energy with complete efficiency, real-world engines necessarily create some level of by-product. This by-product, which is generally harmful to the environment, includes exhaust fumes and evaporative vapors.

Emissions may include such toxic or otherwise harmful materials such as hydrocarbons, nitrogen oxides, carbon monoxide, carbon dioxide, and lead. These emissions may pollute air, land, and water; create health risks for living things; and contribute to global warming or other environmental crises. Vehicle emission standards—as developed, overseen, revised, and enforced in the United States by the Environmental Protection Agency (EPA)—serve to reduce the amount of harmful by-products caused by vehicle engines.

Background

Automobiles and the exhaust they emit are some of the main sources of air pollution and other forms of pollution worldwide. Although most individual vehicles in the United States, when well-maintained, do not create excessive amounts of harmful by-products, the cumulative environmental harm of millions of vehicles can become significant. In overcrowded areas or countries with lax emissions standards, automobiles can significantly damage the environment and contribute to climate change.

Although companies have introduced several new forms of automobiles, including hybrid and electric cars that use electricity to power their engines, the vast majority of automobiles in the early twenty-first century are traditional gasoline-powered models. These vehicles are machines that get power from burning fuel (gasoline or diesel) inside their engines. This fuel is prone to evaporating, which causes some air pollution. However, most air pollution arises from exhaust, a by-product created when the fuel burns inside the vehicle engine.

Gasoline and diesel are chemical compounds called hydrocarbons because they contain hydrogen and carbon. In a perfect scenario, a vehicle engine would convert these chemicals with total efficiency, reducing the amount of pollution they cause. However, no engine works with perfect efficiency, and the fuel-combustion process necessarily creates various types of harmful by-products, referred to as exhaust. Vehicle exhaust generally contains four main types of pollutants. One is hydrocarbons, mainly in the form of fuel molecules that do not combust or only partially combust in an inefficient engine. Another group of pollutants includes nitrogen oxides, caused by atmospheric nitrogen and oxygen reacting to the engine’s activity. Carbon monoxide is a very harmful by-product created when fuel is not fully converted during the combustion process. Finally, carbon dioxide can also result from inefficient vehicle emissions.

Another source of pollution is the evaporation of fuel, which can be more difficult to prevent. Experts have determined that, in high-efficiency modern cars, fuel evaporation may create the majority of the harmful environmental impact. This evaporation most often occurs on hot days when the high temperature warms the gas tank and causes vapors to escape into the air. A similar phenomenon, known as running loss, occurs when the gas tank is heated by the warmth of a running engine. These emissions can occur while the car is in operation or even after it is parked. Evaporation also occurs when drivers refuel their cars and gasoline vapors escape from tanks and pumps. So much vapor can have a cumulatively dangerous effect on the environment.

Overview

The first internal combustion engines—machines that created power by burning gasoline and similar fuels—appeared in the last half of the nineteenth century. These engines remained rare, however, until the rise of the automobile in the early 20th century. At that time, most automobile designers adopted combustion engines for their new inventions. As automobiles caught on and became common sights in towns and cities across the world, combustion engines became the standard for human transportation on land, as well as in sea and air vehicles.

Until well into the twentieth century, people paid little attention to the possible negative effects of their vehicular engine use. Only by the 1950s did true awareness of air pollution and its potentially devastating results become common knowledge and cause for public concern. In 1963, federal legislators in the United States created the Clean Air Act (CAA). This landmark legislation established the idea of regulating the emissions of vehicles and other machines to protect air quality. Over several revisions in 1970 and later years, the CAA ultimately empowered officials to determine standards for safe air quality, examine sources of pollution that threaten this standard, and suggest remedial actions.

Scientists and lawmakers determined that automobile exhaust and fuel evaporation were major culprits in pollution. This pollution, in turn, contributed to serious health risks for people, animals, and plants worldwide, as well as the overall functioning of the planet. For example, hydrocarbon emissions add to the formation of smog, low-level clouds of irritating gases in the air that often surround large urban areas. Toxic hydrocarbons may also increase cancer risk. Nitrogen oxides contribute to damaging acid rain. Carbon monoxide can reduce the body’s ability to carry and use oxygen, possibly resulting in major harm or death. Carbon dioxide is a greenhouse gas that adds to the global warming phenomenon. As understanding of these and other risks developed, regulations against pollution became increasingly stringent.

The CAA gave the Environmental Protection Agency (EPA), which formed in 1970, broad powers in reducing pollution. The EPA was charged with setting the acceptable limits for emissions. After that, it was up to automobile designers to find new ways of meeting these requirements. Design improvements began in the 1970s and included higher-efficiency engines, valves that recirculated exhaust, and charcoal canisters that could collect vapors and prevent them from entering the atmosphere. Machines called catalytic converters debuted in 1975 and helped to cut emissions. That same year, the widespread introduction of unleaded gasoline, which removed the lead content of traditional gasoline, helped to ease the effects of that toxic material on the environment. A 1996 ban on leaded gasoline affirmed unleaded gasoline as the industry standard.

The coming decades saw both stricter requirements and cleaner innovations to meet them. In the early 1980s, manufacturers revised engines to more thoroughly convert their fuels, thus removing more harmful by-products. Computers and sensors aligned to engine activity and helped to maintain optimal performance. Computers played an increasingly important role in tightening engine structure and diagnosing emissions problems. Similarly, structural improvements such as better tailpipes made vehicles better able to control their own emissions.

One important tool in enforcing emissions regulations is the recall. A recall involves an automobile manufacturer offering, or sometimes requiring, a repair, an adjustment, or a modification to an existing automobile. Some recalls have occurred over emissions concerns. These include a 1978 Chrysler recall, a 1995 General Motors recall, a 1998 heavy-duty diesel engine recall, and a 2015 Volkswagen recall. Recalls may cause consumers major inconveniences and cost companies millions of dollars. Some even lead to investigations into possible misdeeds within the company. However, each provides learning opportunities and insights into how to improve emissions controls in future models.

The EPA has detailed lists of regulations for various vehicles, both on-road and non-road varieties. On-road vehicles are broken into several categories. Light-duty passenger vehicles include the cars and trucks that most people use in everyday life. Commercial trucks and buses include heavy-duty vehicles that people use for work, generally to carry numerous passengers or heavy cargo. The third and final category is for motorcycles, light-duty two-wheeled vehicles used on roads for personal transportation. For each of these vehicles, the EPA has established acceptable levels of emissions that may contribute to greenhouse gas, smog, soot, or other forms of airborne pollution. For example, light-duty vehicles are subject to regulations including standards for emissions, both in exhaust and evaporation, and control of toxic or otherwise hazardous pollutants.

The EPA also monitors a wide variety of non-road vehicles. These include ground vehicles not intended for use on standard roads, such as recreational vehicles, as well as locomotives and other rail-based vehicles. The EPA additionally monitors seagoing vehicles that use ignition engines as well as all types of powered aircraft. For each type of vehicle, EPA officials maintain acceptable levels of emissions and methods of testing. The EPA also regulates non-vehicular machines, such as small equipment and tools that use fuels or create by-products that might be harmful to nature.

Together, the stricter emissions requirements and the many improvements in engine efficiency have had a marked effect on air pollution. The average individual vehicle in the United States in the twenty-first century produces far fewer pollutants than earlier models. However, a complication arises in that more people than ever are using automobiles, reducing the overall helpful impact of emissions controls. Scientists and legislators continue to explore the topic. Continued improvements in car engines, along with adoptions of cleaner alternative fuel sources, may provide a long-term solution to the problem.

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