A few years ago, while taking a course in air pollution control technology, I first learned that a small percentage of cars (known as super emitters) are responsible for a large portion of total vehicle emissions of pollutants.  According to a report by the National Research Council, most researchers agree that about 10% of vehicles are responsible for about 50% of the mobile source emissions.  This makes sense intuitively.  At some point, we have all had an encounter with a particularly smoky super emitter - that car or truck driving in front of us or passing by, spewing noxious plumes in its path.

Mechanical causes

Visible plumes of smoke (with the exception of cold start-up in winter) are a sign of mechanical problems.  The color of the smoke coming from the tailpipe indicates what type of pollutant is being produced, providing a clue as to the likely mechanical cause of the emissions.  The chart below, from the San Joaquin Valley Air pollution Control District, shows the most likely causes of black or gray, blue and white smoke in gasoline and diesel engine vehicles.

In the U.S., most of the cars on the road have gasoline engines, and diesel engines are mainly in trucks.  In other countries diesel engines in cars are somewhat more common.  For both types of engines, black or gray smoke is most likely due to incomplete combustion, where fuel is not properly burned and high levels of invisible carbon monoxide are released along with the smoke.  This also results in worse gas mileage and likely engine damage.  Blue smoke results from burning oil, and white smoke has different causes depending on the engine type. 

According to the Australian Office of Environment & Heritage, "routine servicing will eliminate many problems that cause smoke emissions," but "smoke from petrol engine vehicles (most cars) is mainly due to excessive wear."  The repair costs for fixing the possible causes of vehicle smoke listed in the chart above vary quite a bit.  A clogged air filter is cheap to fix, whereas a cracked block or cylinder head is a much costlier repair.

An important decision

If the repair bills for your old car reach the point where they are close to its trade-in value, it might be time to consider getting a different car.  Factors to consider are the car’s age and safety and how frequently it breaks down as well as the cost of repairs versus the cost of a new vehicle.  FirstCarGuide lists several points to consider when deciding whether to repair an old car or buy another, including the following:

• Older, high-mileage vehicles are more likely than newer vehicles to have problems.  Older vehicles also tend to have more serious problems, such as engine and transmission failures, that are expensive to repair. 
• If your car is generally unreliable and is causing you inconvenience and unexpected costs, you may want a newer car that is more dependable and predictable. If your car has a long history of problems, it is not likely to end soon.
• Will the repairs really fix the problems, or will they just temporarily patch the problems? Is it likely that these will be the only repairs needed for a while? Can you afford the cost? If you were to sell or trade the vehicle, could you recover the cost?
• Older cars have fewer safety features than new cars. There’s always the chance that an older car’s safety equipment doesn’t work properly. Do the airbags still work? Is the ABS still protecting you? Has your car been structurally damaged in an accident? 
• Can you afford to buy a car that is substantially newer and better than your old car? Can you afford possible higher insurance rates and taxes? Does your old car have enough resale or trade value to help with the cost of a newer car?

What's not an option?

Doing nothing.  With the exception of vaporized water, the pollutants in visible emissions are harmful to human health and the environment.  Nitrogen oxides, hydrocarbons and resulting ozone are linked to eye, nose, throat and lung irritation in the short-term and respiratory and cardiovascular diseases from chronic exposure. 

Written by :

Elizabeth Klusinske