From an article in E Magazine:

According to Kathryn Phillips, manager of Environmental Defense’s California Clean Air for Life campaign, it [biodiesel] actually increases nitrous oxide (NOX) emissions, which react with other chemicals to create ground-level ozone, or smog, significantly impacting lung development in children.

After glossing over the problem by telling us that “the biodiesel industry is working on methods to reduce NOX via an additive or catalyst,” the author then spends the next 1,310 words telling everyone they should burn it not only in their cars but also in their furnaces.

Although biodiesel is cleaner than heating oil, it is much dirtier than natural gas. It’s not a problem as long as people do not run out and start replacing their natural-gas furnaces with oil furnaces so they can use biodiesel — as is happening with gasoline cars. Replacing a natural-gas furnace with a biodiesel furnace would be a big step backwards from an air-pollution perspective (likewise for replacing a gasoline-powered car with a biodiesel-powered one). Some gasoline cars are on the verge of being zero-emissions vehicles.

All the other downsides to using biodiesel aside, the author also glossed over (or was completely unaware of) just how much more NOX a biodiesel car spews over a conventional gasoline car — a full order of magnitude. There are reasons some states have banned the sale of new diesel cars, and biodiesel spits out 10 percent more NOX than standard diesel.

It is one thing for industrial trucks to use biodiesel. They have to use diesel engines for their higher torque, and with the exception of NOX, biodiesel is cleaner than regular diesel, but thanks to air-pollution controls (that cannot be applied to diesel) it is not cleaner than gasoline-powered cars.

Replacing your gasoline car with one that burns biodiesel is another story. Your neighbors will have to breathe your NOX as you do your part to save the planet from global warming by using biodiesel instead of walking, biking, or just driving less. It’s a trade-off. Just because half the cars in Europe are diesel does not mean they always get things right. Even though France has replaced coal with nukes for about 80% of their electric power, they are still struggling with clean-air problems thanks to all of the diesel cars. From an air-pollution perspective, they would be better off using biodiesel in their cars, but they would be even better off if they drove gas cars that can capitalize on modern air-pollution controls.

The author ends the article with the oft-repeated urban legend that biodiesel exhaust smells like french fries. This is only true if you happen to be burning oil that had been used to cook french fries; otherwise, it has the acrid smell of burnt vegetable oil, which does not appeal to me. I have no problem seeing how something that smells that bad is also bad for my children’s lungs.

By the way, the Europeans are having other biodiesel-related problems:

… while there are no shortages as yet, rapeseed prices have shot up in the past couple of years and there is less available for food producers.

Wow, who could have seen that coming?

Critics say they have nothing to worry about. Just squeeze the water to the other end of the balloon. They can always get their vegetable oil from someplace else (like soybeans or palm oil grown where rainforests used to be).