|Air, Atmosphere and Breathing|
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The Way of Breath
Car Exhaust - Air Pollutants
In cities across the globe, the personal automobile is the single greatest polluter, as emissions from a billion vehicles on the road add up to a planet-wide problem. Driving a private car is a typical citizen's most air polluting activity. The negative effects of automotive emissions are maximum when you sit in traffic surrounded by cars, their engines idling. Everyone sitting in a traffic jam is getting poisoned.
Greenhouse gases are carbon dioxide, methane, nitrous oxide and chlorofluorocarbons (CFCs). These gases act like the glass covering a greenhouse, letting sunlight in but blocking some of the infrared radiation from the earth's surface that carries heat back into space. The gases act like a blanket wherever their concentration increases. Local concentrations increase local heat and increased differences between hotter and colder regions drives weather events into more extreme ranges. Over many years, the total amount of greenhouse gases accumulates and the average temperature of the whole planet is increasing. The planet's thermostat had been set at a pleasant average temperature of 59 degrees (F) for the last 10 thousand years or so and is now rising.
In our view, the main concern should be the effect of heat retention on local climates right now. It is possible to imagine increasingly anomalous weather and increasing loss of life and property from greenhouse gas accumulation with little or no change in the average temperature of the planet, although, we do expect slow progressive increase in average temperatures.
The Combustion Process Gasoline and diesel fuels are mixtures of hydrocarbons (made of hydrogen, oxygen and carbon atoms.) Hydrocarbons are burned by combining with oxygen. Nitrogen and sulphur atoms are also present and combine with oxygen when burned to produce gases. Automotive engines emit several types of pollutants.
Typical Engine Combustion:
Fuel + Air => Hydrocarbons + Nitrogen Oxides + Carbon Dioxide + Carbon Monoxide + water
Hydrocarbon emissions are fragments of fuel molecules, only partially burned. See Toxicity of Benzene and other Hydrocarbons in exhaust.
Hydrocarbons react in the presence of nitrogen oxides and sunlight to form ground-level ozone, a major component of smog. Ozone irritates the eyes, nose, throat and damages the lungs. A number of exhaust hydrocarbons are also toxic, some with the potential to cause cancer.
Nitrogen Oxides Under high pressure and temperature conditions in an engine, nitrogen and oxygen atoms react to form nitrogen oxides. Catalytic converters in car exhaust systems break down heavier nitrogen gases, forming nitrogen dioxide (NO2) - 300 times more potent than carbon dioxide as a greenhouse gas. NO2 makes up about 7.2 percent of the gases that cause global warming. Vehicles with catalytic converters produced nearly half of that NO2. NO2 also originates from nitrogen-based fertilizers and manure from farm animals.
Carbon Monoxide Carbon monoxide (CO) is a colorless, odorless, poisonous gas, a product of incomplete burning of hydrocarbon-based fuels. Carbon monoxide consists of a single carbon atom and a single oxygen atom linked together (CO), the product of incomplete combustion of fuel. Most CO is produced when air-to-fuel ratios are too low in the engine during vehicle starting, when cars are not tuned properly, and at higher altitudes, where thin air reduces the amount of oxygen available for combustion. Two-thirds of the carbon monoxide emissions come from transportation sources, with the largest contribution coming from cars. In urban areas, the passenger vehicle contribution to carbon monoxide pollution can exceed 90%. Read more about Carbon Monoxide
Carbon Dioxide U.S. Environmental Protection Agency (EPA) originally viewed carbon dioxide as a product of "perfect" combustion, but now views CO2 as a pollution concern. Carbon dioxide is a greenhouse gas that traps the earth's heat and contributes to Climate Change
Evaporative Emissions Hydrocarbon pollutants also escape into the air through fuel evaporation - evaporation causes significant hydrocarbon pollution from cars on hot days when ozone levels are highest. Evaporative emissions occur several ways:
Diurnal: Gasoline evaporation increases as the temperature rises during the day, heating the fuel tank and venting gasoline vapors.
Running Loses: The hot engine and exhaust system can vaporize gasoline when the car is running.
Sitting Evaporation: The engine remains hot for a period of time after the car is turned off, and gasoline evaporation continues when the car is parked.
Adding Fuel: Gasoline vapors are always present in fuel tanks. These vapors are forced out when the tank is filled with liquid fuel.
(See Cars and Pollution US EPA Fact Sheet OMS-5)
Benzene is the main toxin in the hydrocarbon fraction of exhaust. Benzene and other less known hydrocarbons are produced in petroleum refining, and are widely used as solvents and as materials in the production of various industrial products and pesticides. Benzene also is found in gasoline and in cigarette smoke. Other environmental sources of benzene include gasoline (filling) stations, underground storage tanks that leak, wastewater from industries that use benzene, chemical spills, and groundwater next to landfills containing benzene. Exposure to benzene can cause cancer, especially leukemias and lymphomas. Benzene has a suppressive effect on bone marrow and it impairs blood cell maturation and amplification.
Polycyclic aromatic hydrocarbon (PAH)
PAHs are a group of chemicals that are formed during the incomplete burning of coal, oil and gas, garbage, or other organic substances. PAHs can be man-made or occur naturally. A few of the PAHs are used in medicines and to make dyes, plastics, and pesticides. They are found throughout the environment in the air, water and soil. There are more than 100 different PAH compounds. Although the health effects of the individual PAHs vary, the following 15 PAHs are considered as a group with similar toxicity: acenaphthene, acenaphthylene, anthracene, benzanthracene, benzopyrene, benzofluoranthene, benzoperylene, benzofluoranthene, chrysene dibenzanthracene, fluoranthene, fluorene, indenopyrene, phenanthrene, pyrene.
Long term solutions require reduced combustion of all kinds. While vehicles with new energy sources such ethanol, biofuels, propane and natural gas can contribute to reduced air pollution, their benefit is limited if vehicle use continues at current intensities. If you pay more money to buy a hybrid car, but drive it more, you have contributed little to solving air pollution problems. If you buy a gas guzzling clunker and use only one gallon of gas to go 15 miles each week, you have contributed more to the solution.
The problem with all alternative fuels is that the manufacture of fuels requires energy, distribution with a manufacturing infrastructure that consume energy, often derived from burning fossil fuels. No alternative fuel is ideal. See Switch to Biofuels
Hydrogen Ultimately cars might burn hydrogen in fuel cells, but despite working prototypes, a hydrogen economy is a distant fantasy. There are many problems to be solved before hydrogen can replace fossil fuels as a portable energy source. The biggest problem is that producing hydrogen requires a large amount of energy. In Canada, there are opportunities to dam rivers and produce electricity with falling water, a non polluting, renewable energy resource. A more problematic energy source would be be nuclear reactors that "burn" uranium or plutonium. Even if new non-polluting energy sources are developed, hydrogen storage and distribution requires a new, very expensive infrastructure that could replace gasoline and diesel fuels.
With once rich countries such as the USA on the verge of bankruptcy and facing the extensive repairs of already aging, derelict infrastructures, adding a new, unprecedented development costs seems unlikely. Unless, of course the priorities in the US shift dramatically. The US, for example, could adopt a sane, smart strategy, reduce its military budget by 50% and invest the money and skills in rebuilding the country's infrastructure with new sustainable energy sources.
Discussions of Environmental Science and Human Ecology were developed by Environmed Research Inc. Sechelt, B.C. Canada. Online Topics are developed in several books by Stephen Gislason MD. These can be found in two catalogues, Alpha Education and Persona Digital Books. Environment Home
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