The Smog Check program has identified Gross Polluter (GP) vehicles as a significant source of smog emissions. Gross Polluter vehicles are chosen through these strategies:

* Vehicles tested at licensed stations which exceed at least one of the gross polluter standards (twice the maximum emission limits)

* Vehicles selected from the High Emitter Profile (HEP) database which have a high probability of failing the Smog Check inspection. 

Once a vehicle is classified as a Gross Polluter it has to initially be tested at a "Test-Only" inspection station. If the vehicle fails this inspection it must undergo repairs and return to a Test-only, Referee or CAP (Consumer Assistance Repair) station for certification.

Vehicles, which are not classified, as gross polluters, do not have to seek a Test-Only inspection and can visit any local smog station. Once again, your DMV documents will state which type of test your vehicle requires.

K. Shafizadeh & D. A. Niemeier Department of Civil & Environmental Engineering, University of California – Davis, USA

Emission cut points are used to classify vehicles as “gross polluters” in inspection and maintenance (I/M) testing in the United States. In this study, we use recent data from California I/M tests to examine how sensitive populations of “gross polluters” change as cut points are modified. Using statistical analyses of emissions test data, we identify a variety of scenarios that have the potential for efficiently removing a significant portion of the exhibited emissions while minimizing the number of vehicles that are classified as “gross polluters” and required to undergo costly repairs. For each scenario, we compute the resulting vehicle populations and impact on emissions. The conclusions of the research provide support for previous findings that suggests that: 1) a “gross polluting” vehicle for one pollutant, such as carbon monoxide (CO), may not necessarily be a “gross polluter” for another pollutant, such as oxides of nitrogen (NOx) and 2) each of the existing required I/M tests yield similar results and it may not be efficient to use both tests in the identification of gross polluters. 

Introduction and study motivation

The State of California defines gross polluters (also commonly known as a “gross emitters”) as those vehicles responsible for more than half of all mobile contributions to smog (BAR, 2003). In general, this results in about 10-15% of the vehicle population being identified as gross polluters. The definition of a gross polluter is based strictly on the 50% of contribution criteria, and millions

Clean air is everyone's job!

Passing Vehicles--Vehicles emitting allowable emissions levels in accordance with their emissions standards.

Failing Vehicles--A failing vehicle emits more than the allowable emissions standards and/or has missing or modified parts. These vehicles usually have a high level of deterioration and/or a significant emissions system defect.

Gross Polluters--Gross Polluters are the worst polluting vehicles on the road. Gross polluters emit at least two times the emissions allowed for a particular model and , in many cases, much more. Gross Polluter standards vary according to the age and type of vehicle. For example, a 1987-92 vehicle that is a Gross Polluter pollutes an average of 18 times more than the average Passing Vehicle for that category. And a 1968-70 vehicle that is a Gross Polluter pollutes an average of four times more than the average Passing Vehicle for that category. These vehicles also usually have a high level of deterioration and major emissions system defects, or they have a tampered emissions system.

If you are considering buying or selling a used car, remember it must first pass a Smog Check. Be careful not to let any money change hands until the seller has provided you with the Vehicle Inspection Report that will tell you if the vehicle has passed its Smog Check inspection.

Smog is a serious health problem in California. According to the California Air Resources Board and the South Coast Air Quality Management District, smog causes decreased breathing ability, inflammation in lung tissue, damage to respiratory cells, an increased risk of cancer, increased asthma attacks, increased chest pains due to a lack of oxygen in the bloodstream of those with heart disease, increased hospital and emergency room admissions and increased infections among children. Even healthy people exposed to smog can experience headaches, fatigue, slow reflexes and dizziness.

Gross Polluters create more smog than all other vehicles. So keep your vehicles well-maintained. It can save you money on gas mileage and major engine failures, extend the life of your vehicle, help you pass your Smog Check, and will allow all Californians to breathe a little easier.

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Last Updated: 02/10/2006