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Name: Colleen E.
Status: Other
Age: 40s
Location: N/A
Country: N/A
Date: March 2004

My question is about smog emissions ratings for new cars. I have been shopping for a new car and specifically am interested in a hybrid. I have noticed that some hybrid cars smog emissions rating is higher than that of a regular gas powered vehicle. For example, the Honda Accord is rated with a .49 smog emission and the Civic Hybrid is rated at .90. Why would a hybrid vehicle smog emissions rating be higher?

First of all, kudos to you for being such an aware consumer.

EPA gives its highest rating to cars that produce less than one pound of smog-forming emissions per 15,000 miles. So, both cars are extremely clean compared to most others on the road. By comparison, the lowest-rated 2004 vehicles put out 63.8 to 121.1 pounds over 15,000 miles. Ironically, six out of the eight vehicles that receive the EPA's lowest rating are also made by Toyota.

Higher combustion temperatures or lean fuel-air mixtures can create extra smog pollutants, even in very efficient engines. The standards for the highest rated vehicles are so tight that they have to use steel fuel tanks because plastic tanks are too permeable and allow tiny but measurable amounts of raw gasoline to reach the atmosphere. In the case of the Honda, if you spill a cup of gas while filling up, you have released more pollution than you would by driving 10,000 miles. So, the differences between the two cars you mention could even be related to their vapor recovery systems, which are unrelated to the pollutants coming out of the exhaust pipe.

However, smog-forming pollutants are not the same as greenhouse gases. The generation of these pollutants is not directly related to fuel economy, although the worst polluters tend to have high fuel consumption too. But, even big vehicles can be very clean when it comes to smog. For instance, the 2004 Cadillac Escalade sold in all states actually produces fewer smog-forming pollutants than the tiny 2004 Honda Insight hybrid sold outside of California. (The California version of the Insight is rated the same as the Escalade.)

Keep in mind, though, that even the higher-emission new vehicles are much cleaner than older models. I seem to recall reading that vehicles like the ones you are interested in produce fewer emissions being driven at 70 mph than a 1966 model does while parked in a garage. This is because the gasoline evaporating in the tank and fuel system in the old car is vented to the atmosphere. Plus, the plastics and paint used in the older car also emit solvent vapors that are absent in new models.

Andy Johnson

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