(4) Pollution

 Air Pollution Causes More than 6 Million Deaths Worldwide


What substances pollute?

Almost any chemical or material from either human or natural sources can pollute.

Natural pollutants

This text emphasizes anthropogenic pollutants (i.e., pollutants produced by human activity), but natural chemicals can also pollute. This happens dramatically when an erupting volcano spews out huge quantities of rocks, ash, chlorine, sulfur dioxide, and other chemicals. Other natural chemicals can pollute too, but sometimes human actions allow natural substances to reach dangerous levels as in the following illustrations:

1. Radon is a naturally radioactive chemical, a gas that arises from transformations occurring in underlying rocks and soil around the world as natural radioactive uranium decays. But levels of radon in outside air are low. It is when radon seeps up into – and concentrates in – human structures that problems may arise. The US EPA ranks radon, associated with human lung cancer, as second only to environmental tobacco smoke as an environmental health risk.

2. Arsenic is natural too and previously was not a problem to people in Bangladesh and India. Their problem had been drinking surface water that was badly contaminated with infectious microbes. To correct this, millions of boreholes were drilled to provide clean drinking water. Unfortunately, arsenic in the rock and soil dissolves into the water in those boreholes. The result has been a massive ongoing poisoning event in which millions suffer from arsenic poisoning.

3. Asbestos too, is natural. But, in El Dorado County, California, population growth led to homes being built in previously unoccupied regions, including areas rich in asbestos deposits. Now asbestos exposure has become a major concern. Chronic exposure also occurs in certain regions of Turkey where naturally high levels of asbestos have led to respiratory diseases and cancer. Up until recent decades, asbestos was also a workplace pollutant.

An introduction to pollutant types

Category Examples

Organic chemicals - Polychlorinated biphenyls (PCBs), oil, many pesticides

Inorganic chemicals - Salts, nitrate, metals and their salts

Organometallic chemicals - Methylmercury, tributyltin, tetraethyl lead

Acids - Sulfuric, nitric, hydrochloric, acetic

Physicala - Eroded soil, trash

Radiological - Radon, radium, uranium

Biological -Microorganisms, pollen

Acids, as well as physical and radioactive pollutants can be either organic or inorganic – sulfuric acid is inorganic, acetic acid (found in vinegar) is organic. Biological pollutants are mostly organic, but contain inorganic components.

Gasoline combustion

Gasoline is primarily composed of hydrocarbons (molecules containing hydrogen and carbon) plus small amounts of contaminants. During combustion, the hydrocarbons are converted into the products shown below, subsequently released in the vehicle’s exhaust. Notice that oxygen (O2) is involved in almost all of the reactions. Waste energy is released as heat.

During combustion, hydrocarbons react with atmospheric oxygen (O2) yielding the products shown:

* The carbon in hydrocarbons carbon dioxide (CO2, a gas)

* The hydrogen in hydrocarbons water (H2O)

Because combustion in a gasoline engine is far from 100% efficient . . .

Hydrocarbons + O2CO2 + H2O + incomplete products of combustion. These include carbon monoxide (CO), soot (fine black carbon particles), volatile organic chemicals (VOCs), and lesser amounts of chemicals including PAHs. (Burning gasoline in a laboratory in an enriched oxygen atmosphere, could force combustion to completion, i.e., to CO2+ H2O.)

The contaminants in gasoline also react with atmospheric O2 during combustion.

* Metals + O2 metal oxides, tiny particulate pollutants

* Sulfur + O2 sulfur dioxide (SO2), a gaseous pollutant

Gasoline has little nitrogen (N2). However, 78% of the atmospheric air in which combustion is occurring is N2. Most of this (>85%) is released unchanged in the car’s exhaust. However, some N2 reacts with atmospheric oxygen: N2 + O2 nitrogen oxides

A natural law tells us that matter is neither created nor destroyed. So we know that the hydrocarbons and other substances in gasoline do not disappear. They are converted to CO2, water, and pollutants. The O2 that reacted with substances in gasoline is conserved too, with most being converted to CO2.

Another natural law tells us that energy is neither created nor destroyed. As gasoline burns, only a small portion of its energy is actually transformed into mechanical energy to power the engine. The rest is “lost” as heat. But, the energy is dissipated, not “lost.” Under certain circumstances, waste energy can be captured and used.


1. Assume that a gallon (3.8 liters) of gasoline weighs ~6 pounds14 (2.7 kg). How then can 20 pounds (9.1 kg) of carbon dioxide be emitted per gallon of gasoline (in the car’s exhaust)?

2. (a) How does the sulfur in gasoline end up as sulfur dioxide? (b) The metals as metal oxides?

3. With the exception of water, all the chemicals in the exhaust of your car are pollutants, more than 20 pounds (9.1 kg) of pollutants. How important is this piece of information? Explain.

Pollutant sources

 “I am, therefore I pollute” is a statement applying to a multitude of processes:

▪ Motor vehicles including cars, buses, airplanes, ships, and off-road vehicles

▪ Chemical and petroleum refineries

▪ Manufacturing facilities

▪ Commercial operations including dry cleaners, bakeries, and garages

▪ Plants generating electric power by burning coal, oil, or natural gas

▪ Agricultural operations growing crops or raising animals

▪ Food processing operations

▪ Mining

▪ Construction and road building

 ▪ Military operations

 ▪ Forestry operations

▪ Municipal operations including drinking water and wastewater treatment, and road maintenance

 ▪ Activities occurring in commercial and municipal buildings, and in private dwellings including, e.g., consumer product use. As population grows, pollution grows. And in wealthy locales, consumption per individual typically grows over time too, and technologies become larger. Thus, without concerted effort to prevent it, pollution and other forms of environmental degradation will also grow.

Pollutant fate and transport

Pollutants move and are transformed Pollutants seldom stay at the point of release.

▪ Pollutants move, are transported, among air, water, soil, and sediments, and often food as well. They often move transboundary: across state and national boundaries traveling with air or water currents. Sometimes, biotransport occurs meaning pollutants are carried in body tissues of migrating animals such as salmon, whales, or birds, or are found in the droppings of migratory birds.

▪ The fate of pollutants: a pollutant is typically transformed into end products different than the chemical form in which it was initially emitted. It may be transformed into chemicals that are no longer pollutants as when biological matter is broken down by microorganisms and incorporated into normal biological material within these organisms. On the other hand, a molecule such as TCDD (“dioxin”) can take years, even decades to be transformed into harmless forms.

▪ The process leading to the final fate can be complex.

Air, soil, and water pollution is greatest at the pollutant source

Although pollutants move, their concentrations are higher near the emission source. Consider dioxins emitted as particulates from an incinerator. The highest fallout of the particulates onto vegetation, soil, and water occurs near that incinerator. However, some dioxins do not fallout, but continue traveling with air currents for long distances before settling out.

 ▪ Wherever they fall, they may contaminate forage or grain that is then eaten by cattle and other animals – and these animals absorb these fat-soluble chemicals into their fat. Humans eating fatty meat such as hamburgers then absorb dioxins into their own fat. Chemicals such as dioxins that move into an organism’s fat may stay for years. This is a temporary “fate.” Eventually, over years the dioxins are slowly broken down and move out of the body.

Some impacts of pollutants occur far from the source

If the amount of pollutant carried in wind or water currents remains high enough, the pollutant can have effects far from where it was emitted.

Water transport

In the year 2000 a Romanian mining operation spilled cyanide and hazardous metals into the Danube River, which joins the Tisza River flowing into Hungary and Yugoslavia. One Yugoslav mayor said that 80% of the fish in the Tisza near his town died. Another stated “The Tisza is a dead river. All life, from algae to trout, has been destroyed.”

▪ A few years earlier an accident at a Swiss facility washed large quantities of chemicals into the Rhine River. These were carried into France and Germany, killing fish and other aquatic life along the way.

Air transport

When a gaseous pollutant mixes evenly with the atmosphere, it can sometimes be carried worldwide. Major examples are stratospheric ozone depletion due to CFCs and global climate change due to CO2. And, because some of these pollutants have long lives, they build up in the atmosphere over time unless their emission sources are removed.

▪ What about pollutants that change their chemical form after emission? Sulfur dioxide and nitrogen oxides (acid-deposition precursors) mix evenly in the atmosphere too.

However, whereas CFCs and CO2 are stable in the atmosphere, sulfur dioxide and nitrogen oxides are transformed from gases into tiny particles. Particles are heavier than air and don’t mix evenly. Still, they can move hundreds, even thousands, of miles before the acid particles finish settling out onto land and water. Interestingly, although acid particles do not travel worldwide, their impact is global. This is true because acidic pollutants (most commonly emitted during the burning of fossil fuels) are released in so many places around the world.

Another characteristic of sulfur dioxide and nitrogen oxides is that they are inorganic chemicals and do not degrade in the same way as most organic pollutants do. Although only small quantities may settle out at any one spot, if emissions continue, the acids build up over time in soil and water. Acid originating in European countries harms forests and lakes in Sweden to the north. Japan’s environment is damaged by coal burning in China. There are other pollutants that also travel thousands of miles, sometimes worldwide, and sometimes have impacts at a far point from the source of emissions.

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