Gasoline or diesel more friendly to the environment?

Dear EarthTalk: I’ve been hearing about the great gas mileage for Volkswagens that use diesel fuel. But is it better for the environment to use diesel or unleaded gasoline?

K. Cronk

Bay City, Mich.

In the past, diesel fuel was always considered dirtier than gasoline. But newer standards regulating sulfur content and improved technology in diesel engines have made diesel somewhat kinder to the environment. Many eco-advocates now tout diesel as a viable and preferable alternative to regular unleaded gasoline.

Where diesel fuel really shines over gasoline is improved fuel economy thanks to its higher “energy densityâ€: Diesel contains more power per liter than gasoline. Today’s diesel engines have 20 to 40 percent better fuel economy than their gasoline counterparts, which some say more than makes up for the fact that they also produce about 15 percent more greenhouse gases. This greater efficiency means that diesel engines emit less carbon monoxide and carbon dioxide and fewer hydrocarbons than gasoline engines.

Diesel’s downside is that it emits larger amounts of nitrogen compounds and particulate matter (soot) that can cause respiratory problems and even cancer. The California Air Resources Board (CARB) attributes 70 percent of that state’s cancer risk from airborne toxins to soot from diesel cars and trucks. Nationwide, studies have shown a 26-percent mortality increase for those living in soot-polluted areas.

But diesel’s dark side is getting a little brighter, thanks to new technologies such as Mercedes-Benz’s BlueTEC system (now used in many VW, Audi and Chrysler diesel models) that filters particulates while improving overall engine performance. The Diesel Technology Forum (DTF), a trade association of carmakers, engine builders and petroleum distributors, reports that technologies now commonplace in new diesel engines reduce the tailpipe output of particulate matter by as much as 90 percent and nitrogen oxides by some 50 percent compared to diesel engines on the road just a decade ago.

Meanwhile, continually improving fuel efficiency standards in the European Union (where the majority of new cars purchased in many member countries use diesel fuel) are forcing carmakers to design more fuel-efficient, less polluting vehicles around the world. After all, there’s no sense in designing better engines for one region with high standards and another for areas with less stringent rules.

For now, consumers looking to buy a new or used car — diesel or otherwise — can see how different models stack up in regard to efficiency and emissions via the FuelEconomy.gov website, a joint effort of the EPA and the U.S. Department of Energy.

Dear EarthTalk: What are the differences between farmed versus wild salmon when it comes to human and environmental health?

Greg Diamond

Nashville, Tenn.

Salmon farming, which involves raising salmon in containers placed underwater near shore, began in Norway about 50 years ago and has since caught on in the United States, Ireland, Canada, Chile and the United Kingdom. Due to the large decline in wild fish from overfishing, many experts see the farming of salmon and other fish as the future of the industry. On the flip side, many marine biologists and ocean advocates fear such a future, citing serious health and ecological implications with so-called “aquaculture.â€

George Mateljan, founder of Health Valley Foods, says that farmed fish are “far inferior†to their wild counterparts. “Despite being much fattier, farmed fish provide less usable beneficial omega 3 fats than wild fish,†he says.

Indeed, U.S. Department of Agriculture research bears out that the fat content of farmed salmon is 30 to 35 percent by weight while wild salmons’ fat content is some 20 percent lower, though with a protein content about 20 percent higher. And farm-raised fish contain higher amounts of pro-inflammatory omega 6 fats instead of the preponderance of healthier omega 3s found in wild fish.  

As for what consumers can do, Suzuki recommends buying only wild-caught salmon and other fish. Whole Foods and other natural foods and high-end grocers, as well as concerned restaurants, will stock wild salmon from Alaska and elsewhere.

CONTACTS: Health Valley Foods, healthvalley.com; USDA, usda.gov; David Suzuki Foundation, davidsuzuki.org.

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