What are Automobile Emissions?

Lori Kilchermann

Automobile emissions are gasses expelled from a vehicle's exhaust system. These automobile emissions contain many types of toxic gasses, many of which can harm the environment as well as cause illness to humans if they are exposed to the emissions for an extended period of time. Catalytic converters and oxygen pumps and sensors installed on the vehicle do their part in keeping automobile emissions to a minimum. Hydrocarbons, carbon monoxide, sulfur oxide and particulate matter such as soot are some of the most prevalent automobile emissions.

Automobiles are a major source of carbon dioxide emissions.
Automobiles are a major source of carbon dioxide emissions.

Exhaust gasses are not the only type of automobile emissions that can cause problems with the environment. Evaporative gasses, such as motor oil fumes, grease burning that evaporates off of a hot running engine, and fumes that come from adding fuel to a vehicle, are also dangerous automobile emissions that must be monitored and controlled. Methane is also a factor in automobile emissions; however, it is nontoxic in nature, and there is debate over the amount of concern that should be attributed to the gas. Most automobile emissions are greenhouse gas-qualified. Put in the most basic terms, this means that the emissions are dangerous or detrimental to the environment.

The EGR valve filters vapors to help prevent excess pollutants from being released in a car's emissions.
The EGR valve filters vapors to help prevent excess pollutants from being released in a car's emissions.

The Positive Crankcase Ventilation (PCV) valve was the first effort of automobile manufacturers designed to address the automobile emissions problem head-on. The PCV valve allows the gasses from the engine's crankcase to be recycled into the intake system. From there, they are introduced into the combustion chamber to be re-ignited. This causes less dangerous emissions to be spewed out of the exhaust and into the atmosphere. The PCV valve was first implemented in the US state of California in 1961 and became standard fare on most vehicles sold in the US by 1964—the PCV valve soon become standard on all vehicles worldwide.

Automobile emissions exit a car through a tailpipe.
Automobile emissions exit a car through a tailpipe.

Automobile emission testing first began in California with the 1966 model year. This was the first attempt anywhere to actually test the tailpipe emissions on a regular basis. By the release of the 1968 vehicle model year, this practice was nationwide in the US. The fuel shortage as well as the ecology push found 1974-released vehicles actually being de-tuned and equipped to reduce engine emissions as well as improve fuel mileage. The catalytic converter made its debut in 1975, and with it came the move to unleaded fuel only—this marked the beginning of an attempt to seriously address the emission problems of new vehicles.

Motor oil fumes are one of several dangerous automobile emissions.
Motor oil fumes are one of several dangerous automobile emissions.

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Discussion Comments


@JessicaLynn - Wow, $60? I bet you'll take your car in on time next time!

Honestly though, I kind of sympathize with people who don't get around to getting their emissions tested in a timely fashion. The last time I had to go, it ended up being a major inconvenience.

First of all, the emissions testing station doesn't have evening hours. Most people work 9-5, so you either have to take off work, or go on Saturday. I went on Saturday last time, and it seemed like everyone else in the whole state had the same idea. It took me about two hours to get my car checked. And my car was fine! What a waste of a perfectly good Saturday afternoon.


@MrsWinslow - I believe most places do require emissions testing. I know in my state, you have to go every three years.

And they're pretty serious about it too! They fine you for not showing up by the date you were supposed to. And if you wait too long, they'll suspend your registration until you get your car tested.

It's kind of a pain, but I know it's for the great good, so to speak. However, that didn't stop me from being late on getting my emissions testing last time. Instead of paying only a few dollars, I ended up paying $60 when everything was all said and done. My car passed the test though!


@MrsWinslow - Those nasty, smelling exhaust emissions bother me, too, but try to have sympathy for people who can't keep up.

I have an elderly Honda Accord whose Check Engine light has been on and off for the last three or four years. I've had it checked out and was told I needed a new catalytic converter.

Well, that's not in the budget! My car isn't belching gobs of smoke, but it would not pass emissions testing if I lived in the next town over. I'm not a bad human being, I just don't have spare wads of cash to throw at something that's not affecting my car's drivability. At least I don't drive the car all that often, which limits the emissions from it.


It drives me bonkers when you see emissions from a vehicle that clearly should have been off the road years ago, just belching smoke and stinking up the air.

I've lived in a couple of metropolitan areas that had emissions testing. You had to bring your car in to make sure the exhaust system was working properly, and they also made sure your "Check Engine" light was not on. (A lot of people don't realize that this light is generally an emissions issue rather than anything else.)

Sure, it's a bit of a pain and a bit of an expense, but I'd like to see more places have it. There's just no excuse for not taking care of your vehicle.

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