What is Emissions Testing?

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  • Written By: Josie Myers
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  • Last Modified Date: 13 September 2019
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Emissions testing checks the levels of hazardous materials that escape from a motor vehicle with a combustion engine. In many areas of the United States, particularly those that are urban or suburban, emissions testing is mandatory. The goal of mandated emissions testing is to cut down on pollutants that are harmful to the environment, with particular focus on improving air quality.

Although new vehicle emissions have been greatly reduced over the last several decades, the threat to the environment, and to human safety, remains a great concern. There are no federally mandated consumer emissions tests. The Environmental Protection Agency (EPA) works in union with individual state entities to recommend and regulate emissions testing.

Standard combustion engine automobiles release a number of pollutants into the environment, some of which are harmful to humans and other living creatures. Hydrocarbons are unburned fuels that create smog as well as potentially contribute to the growth of cancer. Particulates are soot byproducts of fuel that can cause respiratory concerns. Carbon Monoxide is known to reduce blood flow throughout the body, and is particularly dangerous for those with heart disease.

Other pollutants are also threatening to the environment. Carbon Dioxide is a greenhouse gas that is thought to contribute to global warming. Nitrogen Oxide causes smog as well as acid rain.


There are a number of ways that vehicle manufacturers control emissions in order to pass emissions testing. A catalytic converter changes harmful emissions into less harmful ones before releasing them from the vehicle. Exhaust gas recirculation (EGR) valves and positive crankcase ventilation (PCV) systems originate from different areas of the vehicle, but work very similarly. They both filter vapors into the combustion chamber to cool the chamber and prevent the excess pollutants that can be caused by too much heat.

Two of the systems deal specifically with the dangerous vapors created by the evaporation of gasoline. With evaporative controls, a charcoal canister traps the gas evaporation vapors that would otherwise be released into the air. Air injection releases air into the exhaust chamber to cause combustion, that in turn destroys any unburned fuel, and thus prevents the creation of evaporative vapor.

Emissions testing was the result of decades of research into the dangers of vehicle emissions and the struggle to create public awareness about it. The first studies on how motor vehicles contributed to environmental degradation were done during the 1950s. By the 1960s, many car manufacturers had already begun to self-regulate the emissions on their vehicles. The first emissions testing was done in California in the 1960s. Today, most urban areas require testing, a fact that has forced manufacturers to come up with new ways to reduce emissions in order to remain competitive.


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Post 4

If you are interested in taking a look at how sustainable and healthy your city is, I have found a great site called sustain lane. The site does annual rankings of different cities based on a number of different criteria including water quality, air quality, traffic congestion, and the likes. The site even ranks different cities on their local food production and urban planning. I live in Atlanta, and it was interesting to see how my city compared to others.

Post 3

@ PelesTears- I live in Phoenix and we have a problem with air quality. Our air quality is horrible. I think it is partly to do with the location, since the city sits so low and is surrounded by mountainous peaks. However, I think it is mostly due to the fact that phoenix is a sprawling city with little precipitation for most of the year, and the city is built around its car culture. Some days, the air pollution is so bad that my sinuses hurt, and my nose runs nonstop. I hate being that person that is always sniffling, but I love this city's climate. The city does automobile emissions testing, but until they either enforce higher standards, or chop of the dying suburbs, then I think the air quality will always be horrible.

Post 2

Auto emissions testing is a pain in the neck, but it has worked in controlling particulate pollution in many American Cities. I can remember my childhood days in Los Angeles when the smog was really bad. The city had smog warnings for bad air days, and you could hardly see across the Santa Monica Bay. I no longer live in Los Angeles so I am not sure if they still have bad smog days, but the few times I have been back I have notice that the air pollution levels have been much better. I guess it pays to have the highest emission standards in the country.

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