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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	50k 120k	0 0.01	0 0.01	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