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Sometimes you see it; sometimes you smell it. Sometimes you see and smell it. Sometimes you don’t even notice it at all. But whether you notice it or not, there is exhaust coming from your vehicle, and it is contributing to air pollution. 

Air pollution refers to the presence of foreign substances in the air that don’t belong there, or excessive amounts of certain impurities that wouldn't otherwise harm us in moderation. When vehicles burn gasoline or diesel fuel, they emit pollutants. Gasoline fumes escape into the atmosphere even when we do something as simple as removing a gas cap and pumping gasoline into a fuel tank.

Emissions System - Why Does Your Vehicle Have One Image

The days of a simple muffler, pipe, and manifold being all that is necessary to keep your engine running quietly and deliver exhaust away from the vehicle and into the atmosphere are long gone. Today's vehicle emission systems employ a complex system of parts, to not only keep your engine running quietly, but also to reduce the amount of harmful gases that enter the environment. This is the primary reason your vehicle has an emission system.

The emission system significantly reduces harmful gasses created by your vehicle. It works with the exhaust system to minimizes pollutants, and to keep your vehicle's engine operation quiet, efficient, and clean in various operating conditions. Computers, an array of sensors, computerized engine controls, fuel system components, and exhaust components all work together to control your vehicle’s emission output (including the gasoline vapors that escape from the fuel tank). 

By law, your vehicle’s emission system must be maintained and in proper operating condition.  There are currently more than 1.2 billion vehicles in use around the world. That number is projected to be more than two billion by the year 2035. The United States alone has approximately 260 million vehicles in use for its population of 325 million, and that number is growing every day. 

So what pollutants are coming out of these vehicles?

There are four major pollutants generated from driving vehicles:

1. Carbon Monoxide (CO) – This is a product of incomplete combustion. This odorless, colorless, and poisonous gas is formed by the combustion of gasoline when the carbon in fuel doesn't burn completely. If the air/fuel mixture does not have enough oxygen present during combustion, it will not burn completely.

2. Hydrocarbons (HC) - This is a toxic compound of hydrogen and carbon. Hydrocarbons are partially burned or unburned fuel. When combustion does not properly take place, such as when the engine has a misfire, large amounts of hydrocarbons are emitted from the combustion chamber.

3. Nitrogen Oxides (NOx) - When fuel combusts, nitrogen and oxygen react with each other and form in the high temperature and pressure of the engine. In areas of high motor vehicle traffic, such as in large cities or along freeways, the amount of nitrogen oxides emitted into the atmosphere as air pollution can be significant.

4. Particulate Matter (PM) - Particulate matter consists of fine particles, less than one-tenth the diameter of a human hair, such as sulfur dioxide, nitrogen oxides, carbon monoxide, mineral dust, organic matter, and elemental carbon also known as black carbon or soot. These particles give smog its murky color. PM poses a serious threat to human health, as these particles can penetrate deep into the lungs. Diesel exhaust is a major contributor to PM pollution.

Even though pollutants are being created, most modern vehicles have minimal exhaust odor and visibility. This is due in large part to the catalytic converter and precise computer-controlled air-fuel mixtures. However, some vehicles seem to have excessively smelly and visible exhaust fumes and pollute more than others. This can be caused by several issues including the following:

1. Engine mechanical problems - If an engine is burning oil (worn piston rings, faulty valve stem seals or guides, positive crankcase ventilation (PCV) system issues, or just plain worn out), you’ll notice the vehicle has smelly exhaust fumes. You may also notice bluish/gray colored smoke coming from the tailpipe. 

2. Failing catalytic converter - Have you ever been driving along when suddenly you notice the smell of rotten eggs? If so, you’re behind, or near, a vehicle with a failing or failed catalytic converter. Sulfur is found in gasoline and is turned into hydrogen sulfide in the combustion process. However, the catalytic converter changes it into sulfur dioxide, which has no odor at all. As the converter fails, it stops changing hydrogen sulfide into its odorless counterpart, and the result is a strong smell of rotten eggs from the exhaust.

3. Coolant in exhaust - If your tailpipe is emitting a sweet smell and/or a substance that is sticky to touch, it may be engine coolant. Coolant can leak into the combustion chamber and may contaminate engine oil when gaskets fail, or when the engine overheats. White/gray exhaust smoke is another indication that coolant is burning in the combustion chamber.

4. Poor engine performance - If your engine is not running optimally and the exhaust smells like fuel, it’s a sign the air-fuel mixture is not optimal in the engine and too much fuel is being added to too little oxygen resulting in a rich condition. Usually, a check engine light will accompany this issue. Black smoke coming from the tailpipe is also an indication of a rich fuel condition. This condition can damage critical emissions components. 

5. Diesel engine - Diesel exhaust smells much stronger and is more visible than the exhaust from a gasoline engine. Diesel exhaust is generally much darker and contains more particulate matter. 

There are several things you can do to help reduce the emissions coming from your vehicle, and to be proactive against potential problems:

1. Check engine light awareness - Make sure the vehicle’s check engine light, or service engine soon light, operates and is not illuminated when the engine is running. Model-year 1996 and newer vehicles utilize the On-Board Diagnostic (OBD) system to help determine if the vehicle's emission control systems are operating properly. The operation of the check engine light bulb can be determined with the key in the on position without the engine running.

2. Perform regular maintenance - Change your engine oil and filter and the engine air filter as recommended by your vehicle's manufacturer to help your vehicle operate efficiently and reduce its emissions. It is also important to use the type of oil and fuel recommended by the manufacturer for best performance. Dirty oil or a clogged air filter will negatively affect emissions. 

3. Make sure the gas cap is installed and correct - The gas cap should be present unless the vehicle is equipped with a cap-less fuel filler. The rubber seal should not have cracks. It should tighten according to instructions and should be the correct type for the vehicle to avoid excess evaporative emissions. Modern fuel systems are fully sealed to prevent vapors from venting into the atmosphere.

4. Tune-up your vehicle - Be sure to replace your vehicle’s spark plugs as recommended by the manufacturer. This will result in more complete combustion of fuel, improved fuel economy, better performance, and reduced emissions. The air-fuel ratio is critical to maintaining a tuned-up engine. Refer to the owner’s manual for recommended service intervals.

5. Watch for warning signs - Road-weary vehicles can start to show signs of a faulty emission system, including difficulty starting or staying running at idle, loss of power, smelly or visible exhaust, and engine misfires. Many of these warning signs will result in the check engine light coming on. 

If you choose to not pay attention to the proactive action items mentioned above, you will increase your risk of experiencing one or more of the most common causes of a failed emissions test. These include: 

1. Rich air-fuel mixture - This may be due to malfunctioning fuel injectors or a faulty oxygen sensor. Make sure these components are working properly before you take your vehicle for inspection. In extreme cases, a rich-running condition can dump so much raw fuel through the system that it burns out the catalytic converter. 

2. Worn spark plugs - Among other issues, worn spark plugs can also lead to increased emission of gases and a check engine light. Inspect and replace them as necessary.

3. Defects in the evaporative emission control system (EVAP) - If a vehicle's EVAP system is not functioning properly, gasoline vapors will seep out of the vehicle's tank, polluting the atmosphere. Leaking hoses and vents are often the cause of a malfunctioning EVAP system. This can be a tough issue to track down and isolate.

4. Leaking gas cap - This is a pretty simple and straightforward issue that you can easily fix yourself. Many vehicle owners probably don't worry too much about a leaking gas cap, but it is one of the potential reasons for a vehicle to fail an emissions test. Be sure yours is functioning properly. If there are any leaks, replace your gas cap with one that is designed for your vehicle and seals the tank properly.

5. Defective "check engine" light - Sometimes, even if every other component related to controlling your vehicle’s emissions works correctly, you may still fail an emissions test due to a malfunctioning "check engine" light bulb. 

6. Working “check engine” light - If the check engine light bulb is working, and the check engine light is on while the engine is running, you will fail an emissions test.

7. Dirty air filter - High levels of hydrocarbons can be caused by a clogged or dirty air filter, making the air filter another component that should be inspected, and cleaned or replaced if necessary, before an emissions test.

8. Damaged catalytic converter - Inspect the catalytic converter before an emissions test. If the catalytic converter is damaged, it cannot properly convert toxic gases into gases that are not harmful to public health and the environment, and this will cause your vehicle to fail an emissions test.

The percentage of air pollution caused by vehicles is higher in urban areas and higher still near major highways. Fortunately, better fuels and new technologies in vehicles help. The U.S. government has imposed tougher emissions standards, and consumers want better efficiency. According to the EPA, today’s vehicles emit 75 to 90 percent less pollution per mile driven than vehicles made in 1970. Hybrid vehicles, electric vehicles, and alternative fuels will continue to help, but the growing number of people and the 1.2 billion vehicles currently on the road largely offset those improvements.

Do your part to help reduce emissions by making sure your check engine light is not on, performing your vehicle’s maintenance on schedule, making sure your gas cap is present and tight, being aware of how your vehicle is performing, and having your emission system components inspected and tested at least annually to be prepared for any state mandated emissions test and more importantly, to know you are doing your part to help the environment.

Never buy a used vehicle without having the emission system completely inspected to make sure the components are present and operating correctly, the computer and computer warning systems are functioning properly, and the On-Board Diagnostic (OBD) monitors are complete or ready. 

Date Posted: January 14, 2018


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