0.15 Air, water and soil  (Page 11/7)

Air, water and soil

Introduction

Human activities release a variety of substances into the biosphere, many of which negatively affect the environment. Pollutants discharged into the environment can accumulate in the air, water, or soil. Chemicals discharged into the air that have a direct impact on the environment are called primary pollutants . These primary pollutants sometimes react with other chemicals in the air to produce secondary pollutants.

A wide variety of chemicals and organisms are discharged into lakes, rivers and oceans daily. Left untreated, this sewage and industrial waste has a serious impact on the water quality, not only in the immediate area, but also downstream.

Air pollutants

The eight classes of air pollutants are: oxides of carbon, sulfur and nitrogen, volatile organic compounds, suspended particulate matter, photochemical oxidants, radioactive substances and hazardous air pollutants. Oxides of carbon include carbon monoxide (CO) and carbon dioxide (CO2). Carbon monoxide, a primary pollutant, is mainly produced by the incomplete combustion of fossil fuels. It is also present in cigarette smoke. The colorless, odorless gas is poisonous to air-breathing animals. Carbon monoxide binds to hemoglobin, impeding delivery of oxygen to cells. This causes dizziness, nausea, drowsiness, and headaches; at high concentrations it can cause death. Carbon monoxide pollution from automobiles can be reduced through the use of catalytic converters and oxygenated fuels.

Carbon dioxide is produced by the complete combustion of fossil fuels. It is considered a greenhouse gas because it heats up the atmosphere by absorbing infrared radiation. As a result of this characteristic, excess amounts of carbon dioxide in the atmosphere may contribute to global warming. Carbon dioxide can also react with water in the atmosphere and produce slightly acidic rain. Carbon dioxide emissions can be reduced by limiting the amount of fossil fuels burned.

Oxides of sulfur include sulfur dioxide (SO2) and sulfur trioxide (SO3). Sulfur oxides are primarily produced by the combustion of coal and oil. Oxides of sulfur have a characteristic rotten egg odor, and inhalation of them can lead to respiratory system damage. They react with atmospheric water to produce sulfuric acid, which precipitates as acid rain or acid fog. Acid rain is a secondary pollutant that acidifies lakes and streams, rendering the water unfit for aquatic life. It also corrodes metals, and dissolves limestone and marble structures. Oxides of sulfur can be removed from industrial smokestack gases by "scrubbing" the emissions, by electrostatically precipitating the sulfur, by filtration, or by combining them with water, thereby producing sulfuric acid which can be used commercially.

Oxides of nitrogen include: nitric oxide (NO), nitrogen dioxide (NO2), and nitrous oxide (N2O). Nitric oxide is a clear, colorless gas formed during the combustion of fossil fuels. Nitrogen dioxide forms when nitric oxide reacts with atmospheric oxygen; the reddish-brown pungent gas is considered to be a secondary pollutant. Exposure to oxides of nitrogen can cause lung damage, aggravate asthma and bronchitis, and increase susceptibility to the flu and colds. Nitrogen dioxide can combine with atmospheric water to form nitric acid, which is precipitated as acid rain. Nitrogen dioxide is also a key ingredient in the formation of photochemical smog, and nitrous oxide is a greenhouse gas. Automobile emissions of these pollutants can be reduced by catalytic converters which convert them to molecular nitrogen and oxygen.