Automobile emissions
Automobile emissions refer to the pollutants released from vehicles, primarily due to the incomplete combustion of gasoline or diesel fuel, as well as evaporative losses. These emissions include harmful compounds such as carbon monoxide, nitrogen oxides, and hydrocarbons, which significantly impact air quality and contribute to serious health problems, including respiratory and cardiovascular diseases. Additionally, they play a substantial role in climate change, with transportation accounting for a significant percentage of greenhouse gas emissions. Urban areas are particularly affected, as automobile emissions contribute to smog, which can degrade visibility and harm local ecosystems.
Efforts to mitigate these emissions have included the introduction of stringent regulatory standards and the development of cleaner technologies, such as catalytic converters and electric vehicles (EVs). While advancements have been made, the increasing number of vehicles and miles driven continues to challenge air quality improvements. Recent policies in the United States aim to promote EV adoption and further reduce emissions, reflecting a growing recognition of the need to address environmental and health concerns related to automobile use. Overall, automobile emissions remain a critical issue, necessitating ongoing attention and proactive measures at both the local and global levels.
Subject Terms
Automobile emissions
DEFINITION: Combination of vehicular exhaust from incomplete combustion of gasoline or diesel fuel and hydrocarbons that escape these fuels through evaporation
Collectively, the emissions produced by the millions of vehicles on the roads of the world’s major metropolitan areas have serious impacts on air quality and human health. They also represent a significant contribution to greenhouse gas emissions. The US Environmental Protection Agency has described driving a private car as one of the most polluting individual daily activities.
Automobile emissions create ongoing and potentially dangerous environmental problems when gases and particulates are released into the atmosphere at a rate that exceeds the capacity of the atmosphere to dissipate or dispose of them. Motor vehicle emissions are a major component of the smog that blankets many urban areas around the world. The emissions produced by a motor vehicle consist of exhaust (the by-products of incomplete gasoline or diesel fuel combustion) and fuel that evaporates from the vehicle’s fuel tank, engine, and exhaust system during operation, cooldown, and fueling.
Vehicle exhaust contains several problematic compounds. Carbon monoxide, produced by incomplete combustion, reduces the flow of oxygen in the bloodstream. Hydrocarbons, another product of imperfect combustion, are often toxic or carcinogenic. Nitrogen oxides, which are formed when combusting fuel reacts with oxygen in the air, contribute to the formation of acid rain and fine particles that can harm the lungs when breathed in. Together, hydrocarbons and nitrogen oxides react with the heat of sunlight to produce a hazy brown mixture of secondary pollutants. Notable among these pollutants is ground-level ozone, which irritates the eyes and causes damage to the respiratory system. (Nitrogen oxides also readily create ozone by reacting with naturally occurring hydrocarbons produced by trees.) Other secondary pollutants formed by photochemical reactions include the toxic compounds formaldehyde and peroxyacetyl nitrate. Carbon dioxide, a product of complete combustion, is not directly hazardous to human health, but it is chief among the concerns related to anthropogenic (human-generated) climate change.
Impacts on Health and Environment
Environmental problems associated with automobile emissions include deleterious effects on many forms of agriculture and natural forests, reduction in visibility, and damage to building materials such as stone and concrete, metals, rubber, paint, textiles, and plastics. Automobile emissions can cause lung and eye irritation, coughing, chest pain, shallow breathing, and headaches. Automobile-produced air pollution is also a factor contributing to allergies, asthma, emphysema, bronchitis, lung cancer, heart disease, and negative psychological states. Carbon monoxide quickly combines with blood hemoglobin and impairs oxygen delivery to the tissues, particularly in children and older people, causing heart and lung problems. Vehicular emissions and other sources of air pollution cost billions of dollars each year in health care and related expenses.
The increased rate and depth of breathing during physical exertion exposes delicate lung tissue to more polluted air. Research indicates that exercise near a busy freeway may be more harmful than beneficial to the body. Pollution concerns around high-profile sporting events have often highlighted this issue. For example, at the 1984 Summer Olympics in Los Angeles, the evening rush-hour start of the men’s marathon coincided with a stage 2 California health advisory alert, drawing criticism that the organizers of the event were more interested in commercial revenues than in the safety of the athletes and spectators. Later Olympic events were postponed during heavy air-pollution episodes. China faced similar, but more severe, challenges when heavily polluted Beijing hosted the 2008 Summer Olympics. Emergency measures that the city took to improve air quality in time for the games included allowing drivers to use their motor vehicles only every other day, which effectively took more than 1.5 million vehicles off the road daily.
Automobile emissions have been shown to exert their negative effects a considerable distance from the source, depending on atmospheric changes in wind and temperature. Suburbs often exhibit higher levels of pollution than the downtown areas where the emissions are produced. Remote national parks and wilderness areas have had their scenic vistas obscured by haze from distant cities. Fallout of tetraethyl lead from urban automobiles running on leaded gasoline has been observed in oceans and on the Greenland ice sheet. Automobile emissions also have an impact on a global scale, as they are a significant source of greenhouse gases. According to the International Energy Agency (IEA), in 2021 transport contributed 37 percent of carbon dioxide emissions from end-use sectors; road automobiles continued to account for the biggest portion of this number. In the United States, the Environmental Protection Agency (EPA) estimated that transportation contributed 29 percent of the nation's greenhouse gas emissions in 2021, with 58 percent of that figure coming from typical light-duty vehicles.
Efforts to Reduce Emissions
Studies in cities such as London, England, have shown that major improvements in air quality can be achieved in less than ten years in urban areas with favorable climatic conditions through the use of more combustion-efficient engines and cleaner-burning fuels. In the United States, the 1970 amendments to the 1963 Clean Air Act (CAA) introduced automobile emissions standards for hydrocarbons, carbon oxides, and nitrogen oxides and ambient air-quality standards for six pollutants—carbon monoxide, sulfur oxides, nitrogen oxides, particulates, ozone, and lead—to protect human health and the environment. Through the CAA and its amendments of 1970, 1977, and 1990, the EPA established increasingly stringent emissions-control policies for motor vehicles.
Although the EPA sets pollution standards for vehicles, vehicle manufacturers determine how they will meet those standards. Improved engine design, recirculation of exhaust gas to reduce nitrogen oxides, improved evaporative emissions controls, and computerized diagnostic systems have all led to a decline in polluting emissions. One of the most important milestones in the reduction of hydrocarbon and carbon monoxide emissions was the advent of the catalytic converter in 1975. Because lead impedes the catalyst that reduces emissions, unleaded gasoline became widely available at the same time. Ultimately, leaded gasoline was phased out in the United States and in many other countries, with the result that lead concentrations in ambient air were lowered significantly.
Although the vehicle emissions controls implemented in the United States since 1970 have been effective, much of their success has been offset by the increasing numbers of vehicles on the roads and the greater distances driven, as many Americans travel farther from their homes to reach workplaces, schools, and shopping and recreation centers. By 2016 transportation had surpassed power generation as the leading sector for carbon dioxide emissions in the US. Motor vehicle use has also become more widespread in developing countries, where air-quality standards are often more lax than in developed nations.
In the United States, the pollutant associated with vehicle emissions that has been reduced the most has been lead. Ambient concentrations of carbon monoxide and nitrogen oxides have also decreased; however, while they are low in relation to national standards, they remain a matter of concern because of the role they play in producing ozone and particulates and in impairing visibility. Ground-level ozone, toxic hydrocarbons, and particulates continue to be problems—as does carbon dioxide. In May 2009, the EPA and the US Department of Transportation agreed to establish national standards for greenhouse gas emissions and fuel economy for new cars and trucks sold in the United States.
Efforts to reduce automobile emissions have also proven highly dependent on political will. Some politicians have pushed for regulations while others have actively opposed them, claiming they can have negative economic impact. Notably, the Republican administration of President Donald Trump sought, between 2017 and 2020, to roll back existing emissions standards and fuel economy rules for cars and trucks. Environmentalists condemned such moves, and even some automobile manufacturers rejected them, suggesting they would strive to meet stricter standards even if not required by federal law. Some states also continued to enforce tougher regulations, particularly California, which held great influence as a major vehicle market.
Trump administration rollbacks were then overturned by the Democratic administration of President Joe Biden, who was inaugurated in 2021. As adoption of electric vehicles (EVs) had increasingly been seen as a major way to reduce automobile emissions, that same year Biden signed an executive order announcing a goal for the country to have 50 percent of its sales of new vehicles consist of electric vehicles by the year 2030. In early 2023, Biden's administration made further efforts to push automakers toward greater production and sales of EVs when the EPA proposed new, more restrictive emissions rules for automobiles. The following year, the EPA unveiled its final rule on the proposed regulation. Under the new rule, cars produced between 2027 and 2032 would be subject to meeting benchmarks requiring 56 percent of new vehicle sales to be electric by 2023 and 13 percent to be partially electric, or hybrid, vehicles. Supporters of the new regulation noted that it would result in a reduction of over 7 billion tons of carbon emissions into the atmosphere, greatly reducing air pollution that contributes to climate change. With many other countries adopting policies to curb climate change by, in part, reducing automobile emissions and transitioning to greater electric transportation, the IEA reported that there were 26 million electric vehicles on the road in 2022 and that EVs made up 14 percent of all new car sales that year.
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