Automobiles and their toxic by-products:

Have you ever wondered why cars are tested for specific compounds at the emissions centers? Most of us consider the tests an unnecessary evil, generated by bureaucrats with nothing better to do. The results of these tests become important to us only when we have some idea of what these compounds are and how they affect us.

The byproducts of gasoline combustion by all vehicles have critical ramifications on our health as you can learn from the material below.

Although there are dozens of combustion products, this report will only consider the following:

  • Carbon monoxide
  • Ozone
  • Particulate Matter ( PM's)
  • Nitrogen oxides

    Carbon Monoxide

    What is Carbon Monoxide?

    Carbon monoxide is a colorless, odorless, poisonous gas made up of one carbon atom and one oxygen atom.

    2C + O2 ----> 2CO

    How is Carbon Monoxide formed?

    Carbon monoxide is formed by the incomplete combustion of fuel and it is emitted from the tailpipes of cars. Incomplete combustion occurs when there is a low air-to-fuel rations in the engine.

  • two-thirds of the carbon monoxide in the air come from automobiles. In urban areas, the motor vehicle contribution to carbon monoxide pollution can exceed 90%.

    Why is Carbon Monoxide a Health Problem?

  • Carbon monoxide (CO) is an odorless, colorless gas that is readily absorbed by the lungs when inhaled.
  • When inhaled, it attaches to hemoglobin in red blood cells, which forms carboxyhemoglobin (COHb), resulting in the inability of oxygen to attach to the hemoglobin. Thus less oxygen can be transported to cells that need it throughout the body. Unlike oxygen, which is readily picked up in the lungs by RBC's and dropped off where needed, CO binds tightly to the hemoglobin and is not released readily.
  • When this occurs, tissues, especially the brain, suffer from lack of oxygen which causes a number of adverse health effects.
  • These health effects begin as the number of hemoglobin binding sites available for oxygen decreases.
    • The blood's ability to carry oxygen is reduced at COHb levels between 2-30%.
    • Carboxyhemoglobin levels up to 20% may result in headache upon exertion.
    • At levels of 30-40%, dizziness may develop.
    • At levels greater than 50%, seizures and coma may result. At high concentrations in poorly ventilated areas, carbon monoxide can cause coma and death.
  • Heart patients, infants, elderly persons, and individuals with respiratory diseases are very sensitive to carbon monoxide loads.

    What are considered acceptable levels of CO?

    Sources of carbon monoxide are regulated by the EPA under the Clean Air Act.

  • The NAAQS for carbon monoxide is 9 ppm (10 mg/m3) as an eight- hour average, and 35 ppm (40 mg/m3) over a one-hour period.
  • Exposure to concentrations of carbon monoxide at these levels, for these time periods, would be expected to result in carboxyhemoglobin levels of approximately 2% which may result in minor health effects such as becoming exhausted more quickly during exercise but not dizziness or headaches.

    In 1992, CO levels exceeded the Federal air quality standard in 20 U.S. cities, affecting about 14 million people.

    Has Anything Been Done to Control CO Levels?

    State and local governments have been given primary responsibility by the Clean Air Act to regulate pollution from factories, power plants, and other "stationary sources." The EPA has responsibility for "mobile source" pollution control. The EPA has achieved success in reducing CO emissions. In the early 70's, automakers were prompted to improve the basic engine design. In 1975, cars were equipped with catalytic converters which converted CO to CO2. In the early 80's, more sophisticated converters were introduced to help optimize the catalytic converter's efficiency.

    Present automobiles emit 90% less CO than the ones around the 1960's. Because of this the CO levels have dropped, despite the fact that there is an increase in the number of automobiles and an increase in the number of miles they travel.

    What else is being done to contain CO levels?

    CO emissions from vehicles increase tremendously during cold weather, because cars require more fuel to start at cold temperatures, and some control devices operate less efficiently when cold.

    Until 1994, automobiles were tested for CO emissions only at 75 degrees F. But considering the effect of cold weather, the 1990 Clear Air Act calls for 1994, and later, automobiles to meet a CO standard at 20 degrees F as well. Routine Inspection and Maintenance programs by the 1990 Clean Air Act helps identify malfunctioning vehicles emitting excessive CO. Another strategy to reduce CO emissions is to add oxygen-containing compounds to gasoline. This has the effect of "leaning out" the air-to-fuel ratio, thereby promoting complete fuel combustion.


    Automobiles and Ozone in Maryland:

    What is Ozone?

    Ozone is a molecule containing three oxygen atoms. Ozone in the upper atmosphere occurs naturally and it protects life on earth by filtering out UV radiation from the sun. At ground level, ozone however can be toxic.

    Why is Ozone a Health Problem?

  • Ozone damages lung tissue, aggravates respiratory diseases, and makes people more susceptible to respiratory infections. Symptoms of exposure include
    • irritation of the skin, eyes, and mucus membranes
    • increased respiratory rate, shallow breathing, cough,bronchitis, and pulmonary edema
    • fatigue, dizziness, and headache.
    • preliminary evidence exists that it may degrade immune functioning
  • Children and adults with respiratory diseases are very sensitive to ozone.
  • Ozone also inhibits plant growth, reacting and destroying enzymes critical to their functioning..

    Although the current NAAQS for ozone is 0.12 parts per million (ppm) per hour,there are indications that this level should be lowered:

  • generally, concentrations in excess of 0.3 ppm may cause tightness of the chest, dry throat, wheezing, and irritation of the throat and lungs.
  • in those exercising, effects may occur in susceptible persons at levels lower than 0.12 ppm.
  • some epidemiological studies have suggested that ozone concentrations found in urban air may provoke asthmatic episodes in susceptible persons
  • greater than 0.5 ppm may result in headache, drowsiness, loss of coordination, and accumulation of fluid in the lungs (edema).
  • animals exposed to levels between .7 - .9 ppm predisposed or aggravated bacterial infections,
  • Greater than 10 ppm may result in immediate, severe irritation of the lungs,continual coughing, and severe chemical pneumonia.
  • Evidence exists that ozone exposure accelerates the aging process
  • Death may occur from prolonged exposures at 2 ppm or short-term exposures in excess of 10 ppm.

    Nine cities, home to 57 million people in the U.S., are considered "severely" polluted with ozone.

    What about Maryland and CC?

    Maryland is considered to have a history of ozone problems. It ranks 6th in the nation for air pollution infringements.For the situation on ozone in MD see the following sites:

    What happened in the summer of 1995 - why was it so bad.....

    Shows ozone data for different counties in MD

    (taken from MD site above)

    As you can see from the map above, MD and CC have definite ozone problems due to a combination of high vehicular traffic and prevailing wind patterns.

    How is Ozone formed?

    Ozone is formed through a complex set of chemical reactions involving hydrocarbons, oxides of nitrogen, and sunlight.(see section on NOx formation) The rate of reactions depend on both temperature and intensity of the sunlight. Because of this, ozone levels occur most frequently on hot summer afternoons. Hydrocarbons and nitrogen oxides come from industrial and combustion processes. In urban areas, half of these pollutants come from automobiles.

    What Has Been Done to Control Ozone Levels?

    The Clean Air Act of 1970 gives primary responsibility to state and local governments for regulating pollution from power plants, factories, and other sources. EPA regulates "mobile sources."

    The EPA vehicle emission control program has achieved success in reducing both NO and hydrocarbon emissions. Cars today emit 70% less NO and 90% less hydrocarbons than the ones in the 60's. This improvement came when auto manufacturers developed systems capable of capturing excess gasoline vapors and cleansing tailpipe emissions.

    Ozone levels have dropped slightly with the introduction of lower volatility gasoline and improved emission control systems. But the increase in the number of cars on the road and the miles they travel have doubled, therefore increasing ozone levels.


    EPA believes that control of hydrocarbons and NO emissions is the most promising strategy for reducing ozone levels. The federal government will establish more limits on gasoline volatility, control hydrocarbon vapors, and tighten tailpipe emission standards. In some cities the only way to reduce pollutants is to reduce the use of cars.


"This chart shows the projected effect of substituting methanol, ethanol, or natural gas fuel for conventional gasoline in a typical large city. Use of electricity would result in somewhat greater reductions in ozone-forming hydrocarbons; propane in somewhat smaller reductions; and reformulated gasoline in considerably smaller aggressive clean fuels program is adopted, overall hydrocarbon emissions will continue to decline dramatically."

Possible Clean Fuels

  • ALCOHOLS: Methanol and ethanol are high-octane liquefied fuels. Cars with pure alcohol fuels emit 80% to 90% less hydrocarbons.
  • ELECTRICITY: Battery-powered cars have zero hydrocarbon and NO emissions.
  • NATURAL GAS: This emits 85% to 95% less reactive hydrocarbons.
  • REFORMULATED GASOLINE: Reduces hydrocarbon emission by 15%.

    o Automobiles and Particulate Matter less than 10 microns in size (referred to as PM-10 particles)

    Particulates are mixtures of solid and liquid droplets of material that vary in size and origin. Since only very small particles (less than 10 microns in size) can be inhaled into the respiratory tract, they are the most biologically threatening to humans. Particulates of this size are referred to as PM-10 particles. Measured and reported by air pollution monitors, PM-10 particles in urban environments are often composed of soot, acid condensates, and sulfate and nitrate particles.

    Health Effects

    • The American Lung Association report assumed a 1.5% increase in mortality for every 10 microns/m3 increase in PM-10.. Evidence suggests, however, that the association between premature death and the concentration of PM-10 exists at levels well below the current standard.
    • The current EPA standard for PM-10 is 150 microns/m3 for a 24-hour period, and 50 microns/m3 for an annual average. The lower level assessed in the report was 50 microns/ m3 for a 24-hour period, and 30 microns/m3 for an annual average.

    Studies indicate strong positive associations between particulates and mortality not only during episodes of high concentrations of particulates (increases in excess of 100 microns/m3). but as well as at lower levels. Mortality occurs from respiratory diseases and cardiopulmonary diseases.

    • At high levels of PM's, 100 microns/ m3 increase in PM-10 concentrations led to an increase in mortality from obstructive pulmonary disease of 19%, and an increase in mortality from cardiovascular disease of 10%.


    Automobiles and Nitrogen oxides

    How are NOx's produced by vehicles?

    Nitrogen oxides are reactive molecules including nitric oxide (NO),nitrous oxide (N2O) nitrogen dioxide (NO2), nitrogen pentoxide (N2O5) and nitrogen tetroxide (N2O4). Of all of these NO2 is the most important as it is found in highest concentrations and is the most toxic of the lot.

    High temperature combustion of fossil fuels in motor vehicles is the primary source of nitrogen oxides in outdoor air.

    • The air we breathe is 78% N2, but this form of nitrogen is inert - that is non-reactive so it causes no health problems when we breathe it in.
    • The high heat (1210 degrees C) given off by a hot engine is a form of energy that is sufficiently intense enough to break apart the two nitrogens in N2, releasing free N atoms.The second most common molecule found in the air you breather is oxygen (O2), which reacts with the free N to form NO2 .
    • Nitrogen dioxide is a unique air pollutant in that it can absorb UV light energy from the sun. When this occurs the nitrogen dioxide breaks-up into nitrogen oxide (NO), and a free oxygen atom.(O)
    • This free oxygen atom now can combine with an oxygen molecule (O2) to form ozone. O2 + O ---> O3
    • To continue the story, some of the ozone formed can combine with the NO2 to eventually produce after a few more reactions, nitric acid (HNO3).

    Thus the air passing over your hot engine, once exposed to sunlight, can result in a brew of toxins and acids. The health of effects of ozone was covered above, so we can concentrate on NOx's here....

    What are the health impacts of NOx's?

    • Although nitrogen dioxide is detectable by smell at low levels between one and three parts per million (ppm), they do not affect the mucus membrane lining your respiratory tract till they reach levels at about 13 ppm.After exposure of 10- 24ppm experimental animals showed changes in cell appearance, loss of functional cilia, increases in macrophages, and other respiratory reactions.
    • However, studies of asthmatics give evidence that exposure to between 0.1 and 0.3 ppm of nitrogen dioxide may induce broncoconstriction although more research needs to be done. Other studies indicate that it may not be the NOx's themselves, but the acidification of the membranes by NOx's and SOx's in the form of acids that induce damage.

    The NAAQS for nitrogen oxides is 0.053 ppm (100 microns/m3) as an annual average. Concentrations of nitrogen oxides at this level would not be expected to result in any adverse health effects, and thus NOx's are not considered problems outdoors. Indoors however, the levels of NOx's can build up substantially resulting in respiratory problems especially in children.(see page on indoor air pollution)

    Return to Air pollution Menu