Most emission testing centers today check four pollutants: carbon monoxide (CO) and hydrocarbons (HC), nitrogen oxide (NOX) and the "evaporative emissions".
Do you have an old car like a Plymouth Voyager? You are probably concerned with what is emits since your is already quite old and it might emit undesirable colored gasses.
You need to know these emitted dangerous gases to eventually know the right way of maintaining your old exhaust system like the and avoiding these gases at the same time.
Carbon monoxide is the deadliest among pollutants. You cannot see it nor smell it. A concentration of only half a percent (0.5%) CO in the air can make a person unconscious and kill within 10 to 15 minutes. Even very small amount of concentrations as four hundredths of a percent (0.04%) can cause headaches and be life threatening after several hours of exposure.
Never run an engine inside an enclosed garage. Since this is a gas, it diffuses very fast that you cannot even count the seconds of its diffusion. If engine is run inside an enclosed area, chances are 75 percent of carbon dioxide particles are stocked in that area; so you can easily inhale it. Remember that this gas is invisible and odorless. You cannot really tell when it is around.
It is formed when the fuel mixture is rich and there is insufficient oxygen to completely burn all the fuel. Carbon monoxide and fuel mixture has a direct proportionality, which means the richer the fuel mixture, the greater the quantity of CO produced. So high CO emissions indicate incomplete combustion typically caused by several maladjustments.
When the engine is first started, carbon monoxide production is highest because the fuel mixture is richer than normal during this time and the catalytic converter has not yet reached operating temperature. It is therefore the time when it is most dangerous.
Despite these thrilling facts, emission of carbon monoxide can be minimized. By maintaining a balanced to slightly lean fuel mixture, CO is reduced. This just requires careful adjustments on the carburetor idle mixture screws.
Hydrocarbon emissions are unburned gasoline and oil vapors. Though not directly harmful, they are a major contributor to smog and ozone pollution (which are toxic). Hydrocarbons in the atmosphere react with sunlight and break down to form other chemical compounds that irritate the eyes, nasal passages, throat and lungs.
HC emissions, which are usually measured in parts per million (PPM), can go up as a result of a fouled plug or bad plug wire, incorrect carburetor idle adjustment or vacuum leaks that creates a lean mixture that misfires, loss of compression such as a burned or leaky exhaust valve, or engine wear that causes the engine to burn oil Engine wear include the wearing of valve guides, rings and/or cylinders.
Hydrocarbon emissions are controlled in three different ways. One is by maintaining the fuel mixture so it is neither too lean nor too rich to ignite. The second one is by keeping the combustion chamber tightly sealed, and lastly by maintaining the ignition system or changing the plugs periodically. HC that is produced in the engine is burned again in the catalytic converter and changed into water vapor and carbon dioxide.
Nitrogen comprises the most percentage of the air we breathe; about 78 percent. Though normally inert and not directly involved in the combustion process, combustion temperatures above 2500 degrees F cause nitrogen and oxygen to combine and form various compounds called "nitrogen oxide". This mostly occurs when the engine is under load and the throttle is open wide.
Nitrogen oxide can cause irritations in the eye, nose and lungs, headaches and irritability. Higher concentrations can cause bronchitis and they oftentimes aggravate other lung disorders leading to death. Once released in the atmosphere, it reacts with oxygen to form ozone (which is also toxic to breathe) and smog.
Exhaust Gas Recirculation (EGR) is used to reduce the formation of NOX. By circulating again a small amount of exhaust gas back into the intake manifold to dilute the air/fuel mixture, EGR has a "cooling" effect on combustion. This, in turn, puts temperatures below the NOX formation threshold.
High NOX emissions are often times due to a defective EGR valve or some component that controls the operation of the EGR valve. A related sign that usually occurs when EGR is lost is spark knock or detonation while accelerating.
Last of the four pollutants, but still dangerous, are the "evaporative emissions" (EM). EM control system that captures and holds vapors from your fuel tank. The fuel vapors that evaporate from your fuel tank can be another source of smog and ozone pollution. To avoid vapor loss, car manufacturers seal fuel systems for the past twenty years.
The amount of pollution adds up, especially during hot weather, so it is important to make sure the system is functioning properly.
