High-Emitter identification

Remote sensing can identify the worst polluting vehicles circulating in urban areas, enabling government agencies to target only those that cause the biggest problems for air quality. Deploying a set of RSDs all across the urban area in an itinerant scheme, authorities can issue notices of violation, requiring the worst polluting vehicles to return for re-inspection at an inspection station, excluding them from low emission zones or immediately pulling them over for a hands on roadside inspection.

The objective

Very few vehicles are responsible for most of the polluting emissions from road traffic. Our studies show that only 5% of the circulating fleet are responsible for up to 59% of total emissions caused by road traffic.

  • The high-emitters are very few vehicles (1-5% of the circulating fleet). This implies that identifying and correcting them is the most efficient action.
  • They are vehicles emitting up to 200 times more emissions than well-maintained vehicles. Because of that, their contribution to the total emissions emitted by all traffic is enormous.
  • They do not consist of a specific type of vehicle. Any type of vehicle can be a high-emitter. It has been demonstrated that they can be new or old vehicles, diesel or gasoline, cars or vans… Actually, recent data show that up to 25% of high-emitters are less than 6 years old!
  • Any vehicle can be a high-emitter because they are typically vehicles with some defect: missing particle filter, bad admission, non-operating injectors, manipulated SCR… 

How is it done?

A "High Emitter Identification Program" is a program that is established in a given region to identify the worst polluters and take some action on them. Generally, and for legal protection of the vehicle owner, the identification of these vehicles is not punitive, but helps the Authorities to notify the vehicle owner to perform an extraordinary check of his/her vehicle, a practice that is usually contemplated in most international traffic regulations.


The sequence showed above is explained below:

  1. Monitoring: A network of RSDs is deployed all over the city, frequently changing sites to monitor as many locations as possible. Each RSD measures the actual emissions of all vehicles passing by. This process is done in combination with a typical "city traffic characterization" process.
  2. Identification: If the vehicle exceeds certain emission limits, it is identified as a High Emitter. When this identification occurs on the road, an instant warning can be sent to the traffic authority, so that they can force the driver to take the vehicle for an extraordinary emissions inspection.
  3. Notification: The authority notifies the driver or owner of the vehicle of its identification as a High Emitter, and orders a special inspection of the vehicle in an Emissions Inspection Station.
  4. Confirmation: The extraordinary inspection is carried out in a station that has been equipped with adequate instruments for a complete and efficient testing of the polluting emissions. New systems for measuring NOx and PN allow this confirmatory test to be carried out in accordance with the current regulatory procedure.
  5. Correction: If it is confirmed that the vehicle has a defect, it is removed from circulation except for travel to a repair facility. The owner of the vehicle must have it repaired in the workshop before it can be used again.

Some success stories


Without a doubt, the most successful high-emitter identification programs are in the United States, where Opus has been conducting large-scale programs for decades.

High-emitter programs are state-based solutions where the most polluting vehicles are sent to an urgent inspection. In some cases, the opposite is also implemented, where the cleanest vehicles are identified with the RSDs in "Clean Screening" programs. Clean Screen offers owners of the lowest polluting vehicles exemption from their next station-based emission test. Vehicles identified as clean on the road by an RSD then get a Clean Screen notice in the mail. All they need to do is pay the test fees - and they are done. There is no need to visit an inspection station.

Some States apply high-emitter control, while other apply clean screening. Virgnia applies both, in a Total Screening program.

  • Virginia RapidPass complements a decentralized emission inspection program and offers notified candidates a convenient website to redeem their Clean Screen option on-line.
  • Colorado RapidScreen allows notified candidates to pay their inspection fee when they pay their vehicle registration, adding more convenience for motorists.

South Korea

South Korea has measured the emissions of in-use vehicles using remote sensing devices (RSDs) as part of periodic inspection programs since 2013. The Korea Environment Corporation, an environmental service organization attached to the Ministry of Environment, is in responsible for operating remote sensing equipment in South Korea. The South Korean remote sensing program measures the emissions of 2 million to 3 million vehicles per year across 39 different locations.


Some registered vehicles are subject to in-use emission limits. For these vehicles, emission limits for tailpipe concentrations are based on vehicle type and the year of manufacture. When a vehicle’s emissions exceed these limits, defined as three times the standard limit applied during periodic technical inspection, it is classified as a high emitter and a notification is sent to the owner, suggesting that the vehicle be checked. If the same vehicle is observed to exceed RSD emission limits for a second time in a year, the owner receives an order for improvement. The owner is required to stop using the vehicle and get it repaired at a designated inspection and maintenance facility within 15 days from the date of the order for improvement; otherwise, the owner will be subject to a fine. 


Opus RSE

Gaztambide, 45

28015, Madrid (Spain)


Phone: (+34) 91 559 28 68


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