You've probably noticed the recent trend in automotive advertising: There's been a newfound interest in emissions bragging rights, with some automakers touting that their cars meet certain standards, like ULEV or SULEV.
But what does it all mean?
The federal government and California (along with a few other states now) have their own emissions rules, and having the two sets of standards invites confusion. Decades ago, and before any national automotive emissions standards, California mandated its own, more restrictive emissions rules that address the severe smog problems in the state's valleys. Over time, these rules have gradually become not only the standard for the state, but also the standard for the nation.
Though there are many different aspects of vehicle emissions that need to be monitored and limited, the three most important things are considered to be carbon monoxide (CO), oxides of nitrogen (NOx), hydrocarbons (HC), and the accompanying particulate matter. Among these, NOx and particulate matter are most directly associated with smog. Besides being linked to smog problems and changes in the upper atmosphere, each of these pollutants is associated with health risks, including respiratory problems and other long-term effects.
Cars and light trucks that only comply with federal 'Tier 1' emissions (and none of the California standards) are the least-green new cars today, in terms of tailpipe emissions, though they're by no means smoke-belching, raw-gas puffers.
California's TLEV (transitional low-emission) standard is similar to the Tier 1 federal standard, but with tighter limits on hydrocarbons to aid the state's smog-prone valleys.
LEV (low-emission) vehicles adhere to a tighter standard than most passenger cars now meet. The LEV standard for oxides of nitrogen is half that of TLEV and Tier 1, and the allowance of hydrocarbon emissions is further tightened. Cars complying with LEV standards are now widely available nationwide.
ULEV (ultra-low-emission) vehicles further reduce the permissible levels of hydrocarbons and carbon dioxide emissions by 50 percent, compared to LEV. Many models now meet ULEV standards in California, but not necessarily in other states. In simple terms, cars rated ULEV are up to 50 percent cleaner than LEV cars.
SULEV (super-ultra-low-emission) is the new emissions standard to meet. The SULEV standard - about 90 percent cleaner than LEV - is a big leap forward. It requires emissions equipment to perform within the standards for 150,000 miles, and dramatically reduces the allowed amounts of hydrocarbon and carbon dioxide emissions. Only two non-hybrid gasoline-engine vehicles meet SULEV standards for 2002: the Honda Accord (four-cylinder, automatic only) and the Sentra CA (a special California model).
Federal 'Tier 2' standards are on the way in 2004. Most notably, along with California's tighter new minimum requirement called LEV II, they require all vehicles to comply with much tighter limits on hydrocarbons and particulate matter - still not as tight as LEV or ULEV standards, but tight enough to endanger the future of diesels in the U.S.
Currently, increasingly popular 'heavy-duty' pickups and super-size SUVs are classified like commercial trucks and do not have to comply with any passenger-car emissions standards, but beginning with the LEV II standards they will have to meet the same emissions targets.
California and a few other states require a smog index on the window sticker of every new car. A given model's relative pollution can be gauged with a quick look at a bar-graph rating on the window sticker. The index is simply a relative rating of compliance to the state's standards for hydrocarbons, not any other pollutants. Still, it's a good relative comparison to pay attention to when shopping. Just as with actual emissions equipment, automakers will usually include this smog index only in states where it's required.
There are some common misconceptions about emissions that need to be dispelled. Better fuel economy does not necessarily mean lower emissions. Also, more powerful engines do not necessarily pollute more. Often, it's the other way around and the engine is more powerful because its design yields better efficiency. But the aggressive tuning of some top-performance models and special tuner cars means that they barely pass standards and do emit more than their share of pollutants.
One of the best online resources for seeing a summary of which cars meet which standards, see the California Air Resources Board's Buyer's Guide to Cleaner Cars.
Even better, the U.S. EPA now has an excellent online index called the Green Vehicle Guide. Cars are sorted in an easy-to-read format, with a clear explanation of what states the model is offered in, and also a number assigned to it from one to ten, with ten being the 'greenest'.
Today's new cars emit a very small fraction of the pollutants of the cars of a few decades ago. To emphasize the point, according to federal EPA data, a hundred new LEV vehicles will put out less CO and particulate matter than a single average car of the 1950s. But with many times more cars on the road today driving many times more miles, cleaner-burning cars are a necessity for the future, and we must each do our part to consider the cleanest car possible.