Vehicular Exhaust and Air Pollution


Individual tailpipe emissions

Transport and fate in the environment

Measuring exposures

Prevention and control of exposure

Exposure Pathway

Risk assessment

Adverse effects

Harmful Effects

Dose Response

Absorption, Metabolism and Molecular Mechanisms of Action

Organ Sites of Toxicity


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Measuring Exposure

Proper measuring of vehicular emissions for concentration and content is a difficult process. The nature of emissions, the multiple gases and particulate matter, the abundance of vehicles on the roadways, the different regulations on the different makes and models of vehicles, and the fact that the vehicle is in motion, also makes the measuring of emissions difficult. Currently, there are two ways to measure gas emissions. One avenue to measuring emissions is a stationary testing location and the other is a mobile unit. The following page describes each process.

Stationary Unit

Some states require that an automobile be tested once a year to ensure that the vehicle meets the set standards for that car’s year, make and model. Upon arriving to the testing station, the vehicle is checked into a computer system to verify the proper emissions standard for that vehicle. The automobile is then placed on a dynamometer, a treadmill for the vehicle. Depending on the drive train, the car will be placed with either the front wheels (front-wheeled drive cars) or the rear wheels (rear-wheeled drive cars) on the dynamometer. The car is secured to the dynamometer and then accelerated to approximately 25 MPH. A funnel is places as close to the exhaust system (tailpipe) as possible. The funnel siphons the exhaust to a probe, which analyzes the emissions of the vehicle. If the vehicle passes the emission test, the owner pays a fee and is free to go on their way. If the automobile fails, the owner must take the car to a shop and have it tuned up to meet the standards. States that measure emissions usually will not issue license plate tags without passing an emissions test.

Mobile Unit

New technology, produced by NASA, is being used in some states to measure emissions without the owner even knowing about it. The new technology is a mobile unit that uses infrared sensors to analyze vehicle emissions as they pass through the beam. The unit is set up at either a single lane road or an on-ramp to an expressway. As the car passes through the station, an infrared beam is shot across the road to a mirror on the other side. The mirror reflects the beam and a computer retrieves it. Gases and particles absorb the beam and a computer determines the emission concentrations from the returning beam. A camera takes a picture of the license plate verifying the automobiles make and model to set the standard for the emissions. The owner of the vehicle is then notified via mail if they passed or failed the test. The main advantage to this system is that the owner of a vehicle won’t have to set time aside to have an emissions test. However, there seems to be a few drawbacks to the system. Dependant on the flow of traffic and the speed at which vehicles pass, the reliability of the sensor to analyze only one car’s emissions at a time is questionable. If two cars go through the beam within close proximity, the possibility of contamination is high. Also, the infrared beam and sensor could be affected by weather conditions, rendering the information suspect.

Even though the science and technology are there, the measuring of vehicle emissions is still a difficult task. And without a steady, convenient way to measure vehicle emissions, the public will still need to do their part and have their vehicles checked.