Dirty Driving: Top 10 Worst Polluters
- by JIM GORZELANY, ForbesAutos.com
The Hummer H2 might be an obvious target for environmentalists, but unless it’s caked in mud, the hulking sport utility vehicle isn’t the filthiest ride on the road. That distinction goes to another SUV: the Volkswagen Touareg V10 TDI.
The Hummer H2 does make the fifth spot on our list of top 10 worst polluters, thanks to its overall heft and gas-guzzling V8 engine, but what pushes Volkswagen’s Touareg V10 TDI to the very top of the ranking is its large turbo-diesel engine. It dumps so much exhaust into the atmosphere that the U.S. Environmental Protection Agency gives this midsize SUV its lowest air pollution score of 1.
The EPA ranks vehicles on an air pollution scale of 1 to 10, giving a 1 to those that pollute the most and a 10 to those that pollute the least. Most vehicles get an air pollution score of 6. Highly efficient models like the Ford Escape Hybrid, Honda Civic Hybrid and Toyota Prius earn a 9.5, which is currently the highest rating any vehicle gets.
The EPA’s air pollution score is the main criterion for our ranking. It represents the amount of health-damaging, smog-forming airborne pollutants a vehicle emits. These primarily include nitrogen oxide, which combines with hydrocarbons to create smog; carbon monoxide, a colourless, odourless, poisonous gas; particulate matter that creates the black soot that lodges in lungs and deposits on buildings; and formaldehyde, a lung irritant and carcinogen.
In Pictures: Top 10 Worst Polluters
Some heavy-duty pickup trucks and vans pollute more than the Touareg TDI, but they’re intended primarily for commercial use and weren’t included in our consumer-focused list. We also excluded exotic Bentleys, Ferraris and Lamborghinis because they're produced in such limited quantities and so few consumers would consider buying one.
Five other diesel-powered SUVs are right behind the Touareg TDI in our ranking of worst polluters. These include the Jeep Grand Cherokee CRD, the second worst polluter; the Mercedes-Benz GL320 CDI, which is third; and the Mercedes ML320 CDI and R320 CDI, tied for fourth. All of them get an air pollution score of 1.
Not all of the ties on our list were avoidable, but to help break some of them we looked at each vehicle’s carbon footprint, which is the EPA’s way of quantifying other automotive emissions called greenhouse gases. These include carbon dioxide, nitrous oxide and methane. Scientists believe greenhouse gases contribute to global warming.
The primary greenhouse gas is carbon dioxide, but nitrous oxide and methane are also part of the mix.
The Volkswagen Touareg V10 TDI has a carbon footprint of 12.4, which means it emits 12.4 tons of greenhouse gases annually, according to the EPA’s standard calculations based on 15,000 miles (24,000 km) of driving per year. Burning one gallon (3.7 litres) of gasoline emits 20 pounds of carbon dioxide, the EPA says.
The second-place Jeep Grand Cherokee CRD has a carbon footprint of 11.1 annual tons of greenhouse gases and the third-ranked Mercedes GL320 CDI puts out 10.6 tons annually.
Getting Cleaner
Auto emissions are 75 percent to 90 percent cleaner than they were before more stringent federal emissions standards were enacted in 1970, says EPA spokesperson Catherine Milbourn. “Even the worst polluters on the road today are far cleaner than most vehicles were a few decades ago,” she says.
The worst polluter on our list, the Volkswagen Touareg V10 TDI, emits 83 percent less nitrogen oxide and 89 percent less carbon monoxide than the average vehicle built in 1970, according to EPA historical data.
Widespread use of catalytic converters, exhaust gas recirculation, particulate filters and reformulated fuel are the main reasons today’s vehicles pollute far less than their predecessors.
And things will only get better: Some of the biggest polluters on our top 10 list will be cleaning up their acts for the 2009 model year, thanks to the advent of new diesel engine technology.
A new version of Volkswagen's Touareg is among a group of next-generation diesel vehicles from Audi (owned by Volkswagen), BMW, Mercedes-Benz and others. These new and improved diesels will include special catalytic converters and a system that injects urea into the exhaust stream to neutralize pollutants and drastically reduce emissions.
They will start hitting the market late this year and are expected to receive an EPA air pollution score of 6.
Tips for Polluting Less
The easiest way to minimize your carbon footprint with your next car purchase is to choose a model with the best fuel economy possible. But you don’t necessarily have to choose the most frugal car on the lot to do your part for the environment.
Experts say that realizing even minor improvements in fuel economy among the worst polluters on the road is the most efficient way to reduce greenhouse gas emissions overall. For example, choosing a base GMC Yukon with a 5.3-litre V8, which gets 14.7 L/100km overall, instead of the high-end Denali version and its 16.8 L/100km 6.2-litre V8 would save more gasoline per year for the typical driver, and eliminate 1.7 tons of carbon dioxide emissions, says Therese Langer, transportation program director for the American Council for an Energy-Efficient Economy.
“By comparison, achieving the same savings through improvements to a 42-mpg [5.6 L/100km] Honda Civic Hybrid would require a 25-mpg [9.4 L/100km] boost, to 67 mpg [3.5 L/100km],” Langer says.
The EPA currently provides consumers with air pollution scores, fuel-economy estimates and greenhouse-gas-emission ratings for all passenger cars and light-duty trucks at http://www.fueleconomy.gov/ and www.epa.gov/greenvehicles.
A few states have enacted regulations that will require automakers to post labels on vehicles detailing the amount of greenhouse gases each one emits, along with how that model compares to the average of all cars and trucks from its model year. California and Connecticut will begin requiring such labels beginning with 2009 models, and New York will follow suit for 2010 vehicles.
Europe is ahead of the U.S. in requiring that such information be readily accessible to consumers. “In Europe, vehicle specifications now regularly list a model’s CO2 emissions,” says Francois Gravigny, an advisor for market research firm R.L. Polk and Company in Southfield, Mich. “Everybody in Europe knows what their vehicles’ CO2 emissions are.”
Although American consumers are becoming more aware of environmental issues, they’re a long way from choosing vehicles for purely altruistic ecological reasons. “By and large most people believe that they have a right, a God-given American right, to drive whatever car they want and can afford,” says Dr. Charles Kenny, a psychologist and president of The Right Brain People, a psychology research firm based in Cordova, Tenn. “Americans still have a love affair with their vehicles, which are associated in their minds with freedom and independence."
Pollution Versus Greenhouse Gases
Super-high-output versions of Mercedes’ full-size CL-Class coupes and S-Class sedans tied BMW’s M5 sedan and M6 coupe for 10th place. All of those models have a decent air pollution score of 6. But their carbon footprint of 14.1 annual tons of greenhouse gases is among the highest of any non-commercial passenger vehicle.
Generally speaking, the lower the fuel efficiency of a vehicle, the higher its carbon footprint will be.
So it’s the Mercedes’ massive V12 engines and the BMWs’ race-bred V10 engines — built to chug fuel for top acceleration and speed — that are their downfall. These engines get an estimated 11 miles per gallon (21.4 L/100km) in the city and 17 miles per gallon (13.8 L/100km) on the highway, which in turn creates the high carbon footprint.
Diesel engines tend to be more fuel-efficient than comparably sized gasoline engines. So the Jeep Grand Cherokee CRD and Volkswagen Touareg V10 TDI actually create smaller carbon footprints — 11.1 and 12.1, respectively — than the BMW and Mercedes performance cars because their diesel engines get better mileage: 17 mpg (13.8 L/100km) city/22 mpg (10.7 L/100km) highway for the Jeep and 15 mpg (15.7 L/100km) city/20 mpg (11.8 L/100km) highway for the Volkswagen.
But these same diesel engines put the Jeep and Volkswagen SUVs at the top of the worst-polluters overall because they emit more smog-forming emissions, earning the EPA’s lowest possible air pollution score. The EPA says air pollution scores are more critical than carbon footprints because they quantify exhaust emissions that directly impact human health, as opposed to greenhouse gas emissions, which affect climate change.
The U.S. Department of Energy estimates that greenhouse gas emissions from burning fossil fuels increased by 1.6 percent nationwide last year, amounting to nearly 6 billion metric tons of carbon dioxide accumulating in the atmosphere.
Motor vehicles are the largest source of carbon dioxide emissions, accounting for 51 percent, according to the EPA.
Slow-Selling Polluters
Many of the vehicles on our list are sold in relatively small numbers.
Volkswagen expects the V10 TDI version of its Touareg SUV to account for only about 10 percent of all Touareg sales for the 2008 model year, says Keith Price, a Volkswagen spokesperson. Most Touaregs are sold with gasoline-powered V6 or V8 engines. Only 2,835 Touareg V10 TDI models were sold in the United States through the end of March, according to Volkswagen sales data.
Likewise, the BMW and Mercedes-Benz cars on the list are low-volume high-performance variants of more common models, which get better gas mileage and pollute less. BMW sells between 7,000 and 15,000 high-performance "M" models a year — only about 2 percent to 5 percent of the company's total sales.
Mercedes sells around 10,000 high-performance AMG cars each year, equal to roughly 4 percent of sales nationwide.
About Our Ranking
Our list of Top 10 Worst Polluters is based on the EPA's air pollution score — a scale of 1 to 10 where higher is better — and carbon footprint ratings, which measure "annual tons of greenhouse gases." The air pollution scores take precedence because they measure the most harmful emissions. We used the carbon footprints as tie-breakers.
Some vehicles on the list are offered with various engines and transmissions. The variants listed have the worst scores. All vehicles in the slideshow are 2008 models.
In Pictures: Top 10 Worst Polluters
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