Do hybrid cars cause pollution?

By: John Fuller

The angle on hybrid cars usually emphasizes their greenness, but do they cause pollution?
The angle on hybrid cars usually emphasizes their greenness, but do they cause pollution?
David McNew/Getty Images

In big cities where people are packed close together, streets and roads are twisted and traffic jams are inescapable during rush hours, smoggy skies can be a persistent problem. A muggy haze often builds up around most metropolitan areas, especially during the hot summer months, posing health risks for citizens. Smog may give skylines their beautiful, colored sunrises and sunsets, but it also highlights a deeper problem that some areas have with pollution.

Although smog is formed by several different sources, including power plants, industrial processes and various chemicals, one of the main causes of smog is vehicle emissions. The exhaust coming out of our cars' tailpipes, which consists of gases such as nitrous oxides, floats up into the atmosphere. When these gases combine with volatile organic compounds, smog forms. And smog in cities is just a small part of the bigger problem of global warming -- cars in the United States contribute more than one-fifth of the nation's carbon dioxide [source: Environmental Defense Fund].


The realization that current car technology coupled with a heavy reliance on fossil fuels is dangerous for the future of the environment has led many drivers to consider more fuel-efficient vehicles as an alternative to conventional cars. Although there are several different options drivers can consider when looking at alternative fuel vehicles, the most prominent type of car that has captured the public's attention is the hybrid car.

Advertising campaigns and articles often highlight the fuel efficiency and eco-friendly driving technology that hybrids offer. Although the technology varies from one hybrid model to another, most hybrid cars pair a conventional gasoline engine with an efficient electric motor that's powered by a battery. This allows drivers to stretch out how much gas a hybrid burns in between commutes, reducing emissions and saving money at the pump.

But if they're using gasoline, don't hybrid cars still cause pollution? So, how green is so-called green driving, anyway?

Hybrid Car Production Pollution

A significant amount of energy goes into producing hybrid cars, but it's no more than what it takes to make conventional cars.
A significant amount of energy goes into producing hybrid cars, but it's no more than what it takes to make conventional cars.
AP Photo/James Crisp

One point many people don't always consider when thinking about consumer products is how much energy is expended to actually make them and move them around. For instance, when supporters of green driving recommend buying food locally they're stressing the fact that many foods are shipped long distances to get to various neighborhood supermarkets. It requires burning lots of gasoline or diesel fuel to transport that food such a long distance, which only increases the suppliers' carbon footprint. If more people bought food locally, however, that food would have shorter distances to travel, and those that deliver the goods would burn less fuel in the process.

Of course, it takes a lot of energy and resources to make a car -- and that doesn't exclude fuel-efficient vehicles like hybrid cars either. If you've ever seen pictures or video footage of an auto manufacturing plant, you'll see not only plenty of trained workers surveying the progress but also a complex labyrinth of machines. All of the parts that make up the car have to be built and forged, and it takes a significant amount of electricity and other sources of power to do this.


So, is hybrid car production pollution really a big deal? This topic actually caught the attention of the media and the public in 2007, when CNW Marketing Research, Inc. issued a report called "Dust to Dust: The Energy Cost of New Vehicles from Concept to Disposal." The paper claimed to calculate a dollar value for all of the energy necessary to create, build operate and dispose of a vehicle, and it made the surprising claim that the Toyota Prius costs more over the course of its lifetime than a Hummer H3. This, of course, confused and dismayed Prius drivers, since Toyota emphasized fuel efficiency and eco-friendly driving while marketing the hybrid to them.

After blogs and online newspapers began citing the paper and spreading its information around, several publications quickly criticized the findings from CNW for poor analysis and lack of peer review. While "Dust to Dust" claimed that most of the energy used by a vehicle came from its design and production, several other studies have found that 80 to 90 percent of a vehicle's energy is used during operation -- in other words, when you're driving it [source: Gleick].

At the very most, it takes 13 percent of the vehicle's lifetime energy to actually produce the car, whether it's a hybrid or a Hummer, and most carmakers are finding ways to reduce their environmental impact during the design and production phase by replacing hazardous substances like lead and hexavalent chromium with more sustainable materials.

Hybrid Car Emissions Pollution

Hybrid cars, when using the gas engine, create pollution like any other conventional vehicle. The use of an electric motor, however, cuts down on that pollution.
Hybrid cars, when using the gas engine, create pollution like any other conventional vehicle. The use of an electric motor, however, cuts down on that pollution.
AP Photo/Reed Saxon

The simple answer to the question of whether or not hybrid cars cause pollution is: Yes, of course they do. The majority of hybrid cars in production and on the road are gas-electric hybrids, and they burn the same kind of fuel used in conventional, gas-powered cars. Hybrid car emissions pollution is a real thing, but what makes these fuel-efficient vehicles attractive to people interested in eco-friendly driving is how much less pollution they cause in comparison to conventional cars.

What sets hybrid cars apart from other cars on the road is how (and how often) the gas engine actually powers the vehicle. Although there are several different ways to divide power between the gas engine and the electric motor, the gas engine in a hybrid car will usually kick in at higher speeds. For example, gas engines generally provide more horsepower than electric motors, so they're necessary for trips along the highway where speeds reach 45 miles per hour (72.4 kilometers per hour) or faster. Of course, that speed varies from vehicle to vehicle and is even dependent on how aggressive the driver accelerates.


To increase fuel efficiency and promote green driving, however, the electric motor in a hybrid car operates at lower vehicle speeds. This is one of the reasons why many advocates of hybrid cars feel that the vehicles are ideal for city driving, where people don't have to drive long distances and speed limits are typically much lower. The electric motor can also provide additional power during acceleration or when a hybrid is climbing a steep incline. Most hybrid cars also don't have to plug into a power source, since the gasoline engine works to charge the battery.

These elements work together to significantly reduce the amount of pollutants hybrid cars release into the environment. When using the gasoline engine, yes, a hybrid will create emissions like any other vehicle; however, the assistance of electric power significantly reduces the amount of pollutants a car produces over its lifetime.

Hybrid Car Batteries

Although lead and nickel metal batteries are still prevalent, less toxic lithium-ion batteries could be the future for hybrid car batteries.
Although lead and nickel metal batteries are still prevalent, less toxic lithium-ion batteries could be the future for hybrid car batteries.
AP Photo/Katsumi Kasahara

Eco-conscious drivers are buying hybrid cars and other fuel-efficient vehicles for their lower emissions. The combination of a smaller gasoline engine for power, an electric motor for fuel economy and the promise of so-called green driving have proven to be successful incentives for consumers looking to save money on fuel and do their part to help out the environment. But increased awareness about the environmental impact vehicles and vehicle parts have on the Earth has led drivers to shift their concern from fuel efficiency to something else entirely -- hybrid car batteries.

The batteries in hybrid cars are responsible for the better fuel economy that's become central to the technology. They power the electric motor, which typically propels a hybrid car at lower speeds. This puts less pressure on the gasoline engine and stretches out the amount of fuel a vehicle burns in between trips to the gas station.


But the chemical material that makes up all car batteries, whether it's a conventional car or a hybrid, is typically toxic. Currently, there are far fewer hybrid cars on the road than conventional cars; however, concerns have been raised that if the number of hybrid cars increase, landfills will soon overflow with toxic batteries that are full of corrosive and carcinogenic materials.

There are three major types of batteries that companies use or are considering for use in hybrid cars: lead-acid, nickel-metal hydride (NiMH) and lithium-ion (Li-ion). By far, lead-acid is considered the most toxic of the three, and on top of that it's also extremely heavy, reducing some of the fuel efficiency gains from the electric motor. Lead-acid is becoming less of a contender in the hybrid car battery market and is being replaced by nickel-metal hydride. Nickel is less toxic than lead, but it's not without its own problems -- it's potentially carcinogenic and the mining process is considered hazardous. Since they're the least toxic, many consider lithium-ion batteries to be the next step for hybrid car batteries. In fact, car companies are investing millions of dollars in research for a working hybrid car battery that uses the same kind of power currently found in laptops and MP3 players.

For lots more information about hybrid cars and eco-friendly driving, follow the links on the next page.

Lots More Information

Related HowStuffWorks Articles

  • Environmental Defense Fund. "Time to Cut Pollution From America's Autos." Sept. 7, 2007. (May 11, 2009)
  • Gleick, Dr. Peter H. "Hummer versus Prius: "Dust to Dust" Report Misleads the Media and Public with Bad Science." Pacific Institute. May 2007. (May 11, 2009)
  • "Hybrid Battery Toxicity." April 8, 2006. (May 11, 2009)
  • Pullen, K. "Hybrid vehicle emissions." Aug. 11, 2007. (May 11, 2009)
  • Sierra Club. "Prius Versus Hummer: A Nickel for Your Thoughts." Nov. 1, 2007. (May 11, 2009)
  • Sierra Club. "Smog and Ozone Pollution." July 2, 2007. (May 11, 2009)
  • "Hybrid Synergy View Newsletter: Heard the one about the Hummer?"September 2007. (May 11, 2009)