Untangling U.S. Vehicle Emissions Regulations


  • Exhaust Smoke

    Exhaust Smoke

    Automotive emissions standards have grown so increasingly stringent since the introduction of Tier 2 and LEV 2 standards that sooty black exhaust pipes are becoming a thing of the past. | March 18, 2010

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In Part I we described the five major automotive emissions categories and U.S. governmental agencies responsible for the regulation of exhaust by-products. Now let's take a closer look at the allowable limits of those emissions.

To recap, Tier 2 is the set of federal emissions regulations set forth by the Environmental Protection Agency, and LEV 2 describes the regulations prescribed by California's Air Resources Board (CARB).

The Bins That Comprise Tier 2
Eight "permanent" certification levels, known as bins, define the Tier 2 regulations associated with the control of each of the five pollutants. Each bin allows for different degrees of acceptance of those pollutants — bin 8 allows the most emissions; bin 1 allows none.

Bins 9-11 are "temporary" bins, which exist only during the phase-in period of Tier 2 standards. Each permanent bin requires that the vehicle comply at 50,000 miles and meet a somewhat more relaxed standard at 120,000 miles, as shown below.

Tier 2 Emissions Limits for Passenger Cars and Light-Duty Trucks (grams/mile)

Higher Emissions Lower Emissions
    Bin 8 Bin 7 Bin 6 Bin 5 Bin 4 Bin 3 Bin 2
NMOG 50k
120k
0.100
0.125
0.075
0.090
0.075
0.090
0.075
0.090

0.070

0.055

0.010
CO 50k
120k
3.4
4.2
3.4
4.2
3.4
4.2
3.4
4.2

2.1

2.1

2.1
NOx 50k
120k
0.14
0.20
0.11
0.15
0.08
0.10
0.05
0.07

0.04

0.03

0.02
PM 120k 0.02 0.02 0.01 0.01 0.01 0.01 0.01
HCHO 50k
120k
0.015
0.018
0.015
0.018
0.015
0.018
0.015
0.018

0.011

0.011

0.004

How These Different Bins Work
A tier is a fleet-averaged emissions standard. Once Tier 2 is fully implemented in 2009, an automaker's fleet must average no more than 0.07 gram per mile of NOx. (This is equivalent to the NOx level of bin 5.)

Automakers can sell as many "dirty" bin 8 cars as they choose, provided they are balanced by sales of an appropriate number of bin 4 (or cleaner) vehicles in order to achieve the required average. It's like being able to use an "A" in gym class to offset the "C" you got in math since they average to a "B."

"Dirty" is a relative term. Bin 8 — again, the "dirtiest" of all Tier 2 bins — allows only a fraction of the emissions permitted just 10 years ago under Tier 1.

These requirements allow plenty of room for carrying NOx credits over from previous years and for trading or selling credits to other manufacturers within this paradigm. We could devote an entire Web site to explaining that, but suffice it to say that the ultimate intent of the credit program is to ensure that air quality meets an overall standard on a yearly basis.

Emissions Measured on Two Driving Schedules
Different driving conditions produce different amounts of emissions, so the EPA measures the above pollutants during two very specific driving schedules intended to represent city driving and highway conditions.

Well, sort of. The EPA is rethinking those driving cycles, as they were originally created decades ago and do not accurately reflect today's driving conditions.

Where CARB's LEV 2 Regulations Fit in
Conceptually, CARB's LEV 2 standards — the current standards — use Tier 2 as a starting point and then tighten the screws down further.

Most LEV 2 categories are more stringent than the corresponding Tier 2 limit. In fact, the most lenient of LEV 2's categories, Low Emission Vehicle (LEV), is equivalent to Tier 2, bin 5.

LEV 2 Emissions Limits for Passenger Cars and Light-Duty Trucks (grams/mile)

Higher Emissions Lower Emissions
    LEV ULEV SULEV ZEV
NMOG 50k
120k
0.075
0.090
0.040
0.055

0.010
0
0
CO 50k
120k
3.4
4.2
1.7
2.1

1.0
0
0
NOx 50k
120k
0.05
0.07
0.05
0.07

0.02
0
0
PM 50k120k 00.01 00.01 0.01 0
0
HCHO 50k
120k
0.015
0.018
0.008
0.011

0.004
0
0

The remaining LEV 2 categories consist of Ultra Low Emission Vehicle (ULEV), Super Ultra Low Emission Vehicle (SULEV) and ZEV (Zero Emission Vehicle).

A manufacturer wishing to sell vehicles in the states that abide by California's emissions standards can certify to any of the above LEV 2 categories they choose, provided that their entire fleet meets prescribed average NMOG limits. The allowable NMOG is an ever-stricter target, finally bottoming out at 0.035 gram per mile in 2010. This idea parallels Tier 2's fleet-averaged NOx limit.

But Wait, There's More
LEV 2 originally required 10 percent of new cars to be classifieds as ZEVs, which were intended to be essentially battery-powered electric vehicles (EVs). When it became apparent the limitations of existing battery technology would not allow a marketable electric vehicle to be produced, CARB revised its ZEV mandate to include non-battery EVs.

Within the ZEV category above, there are six subcategories. All of these entitle an automaker to receive credits toward the ZEV requirement:

  • PZEV (Partial Zero Emission Vehicle) — a rating reserved for cars that meet both SULEV standards and a near-zero evaporative emissions standard and is warranted for 15 years/150,000 miles.
  • AT-PZEV (Advanced Technology Partial Zero Emission Vehicle) — these are PZEVs that also utilize alternative fuel, electric drives or other advanced technology
  • NEV (Neighborhood Electric Vehicle) — think "golf cart on steroids"
  • FFEV (Full-Function Electric Vehicle) — larger than an NEV and capable of normal-car duties, but with limited range
  • CEV (City Electric Vehicle) — sized between an NEV and an FFEV but legal to run on freeways

PZEV and AT-PZEV have emissions equivalent to or less than the power plant emissions associated with battery EVs. Thus, they can be used to fulfill up to 60 percent of an automaker's ZEV requirement. The remainder of an automaker's ZEV requirement must be comprised of "pure" ZEVs.

PZEVs are typically gasoline-fueled vehicles equipped with comprehensive emissions controls. Most AT-PZEVs are hybrids or alternative-fuel vehicles. In model-year 2008, a total of 56 models are classified as PZEV and six of them are AT-PZEVs.

Ever-Changing Paradigm
Emissions regulations are always evolving as automakers and the enforcing entities learn more about health, weather and the impact of emissions on both. These regulations keep everyone on their toes, advance the state of the art in vehicle technology, and help keep the air cleaner.

Now if we could all agree on a worldwide standard, we'd be making real progress. A reduction in the number of acronyms wouldn't hurt, either.

2008 Model Emissions Ratings
BMW 328i Sedan PZEV
BMW 328i Coupe PZEV
BMW 328i Convertible PZEV
BMW 328xi Sedan PZEV
BMW 328xi Coupe PZEV
Chrysler Sebring PZEV
Dodge Avenger PZEV
Ford Focus PZEV
Ford Fusion PZEV
Mercury Milan PZEV
Ford Escape Hybrid 2WD/4WD AT-PZEV
Mercury Mariner Hybrid 2WD/4WD AT-PZEV
Mazda Tribute Hybrid 2WD/4WD AT-PZEV
Ford Taurus PZEV
Ford Taurus AWD PZEV
Ford Taurus X PZEV
Ford Taurus AWD PZEV
Mercury Sable PZEV
Mercury Sable AWD PZEV
Buick Lucerne PZEV
Buick Lacrosse PZEV
Pontiac Grand Prix PZEV
Chevrolet Impala PZEV
Chevrolet Cobalt PZEV
Pontiac G5 PZEV
Honda Civic Hybrid AT-PZEV
Honda Civic GX PZEV
Honda Accord 2.4-liter PZEV
Honda Accord 3.5-liter PZEV
Hyundai Elantra PZEV
Kia Spectra PZEV
Mazda Mazda3 2.0-liter PZEV
Mazda Mazda3 2.3-liter PZEV
Mazda Mazda6 2.3-liter PZEV
Mercedes-Benz E350 PZEV
Mercedes-Benz C350 PZEV
Mitsubishi Lancer PZEV
Mitsubishi Outlander PZEV
Mitsubishi Galant PZEV
Nissan Altima 2.5L PZEV
Nissan Altima Coupe 2.5L PZEV
Nissan Altima Hybrid PZEV
Subaru Forester 2.5X PZEV
Subaru Forester 2.5XS Ltd. PZEV
Subaru Legacy Wagon 2.5i PZEV
Subaru Outback Wagon Base PZEV
Subaru Outback Wagon Ltd PZEV
Toyota Camry 2.4L PZEV
Toyota Prius AT-PZEV
Toyota Camry Hybrid AT-PZEV
Volkswagen Jetta PZEV
Volkswagen Jetta Sportswagon PZEV
Volkswagen Rabbit PZEV
Volkswagen New Beetle PZEV
Volkswagen New Beetle Convertible PZEV
Volvo S40 2.4i PZEV
Volvo V50 2.4i PZEV

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