What is an Environmental Pollutant? A pollutant is any form of energy or matter causing pollution. In air pollution the pollutants include gases, and solid and liquid particles of both organic and inorganic chemical classification. Water Pollution includes presence of disease-producing (pathogenic) bacteria and viruses (biological pollution) and of undesirable ions and compounds in solution (chemical pollution). Presence of solids causing turbidity may be included as forms of water pollution. Thermal Pollution of air and water, a form of energy infusion, raises the quantity of sensible heat in those fluids to abnormally high levels. Noise Pollution illustrates energy infusion into the environment by sound wave transmission.
Particulate Matter in the Atmosphere: The contents of the atmosphere fall into two basic categories: Particulate matter and gases. Particulate matter consists of particles of matter in either the liquid state or the solid state. In the language of air pollution science, these particles are called Particulates. Particulate matter injected into the atmosphere is of both Man-made and natural origins.
Particulate matter may include sea salt crystals, mineral dust, and volcanic dust. These particulates play a vital role in the atmospheric processes by serving as nuclei of moisture condensation to form clouds. Another class of natural solid particulate matter is smoke from forest fires, and grass fires. Living plants release pollens and spores into the air. These are organic compounds. From forest fires certain hydrocarbon compounds called terpenes are also released into the atmosphere in the form of minute droplets.
These compounds are important in producing atmospheric haze that builds up naturally within stagnant air masses far from industrial pollution sources. Man-made particulate matter comes from many sources but the major source is the combustion of hydrocarbon fuels – petroleum products, coal, peat, and wood. Combustion of solid wastes is another source.
Other kinds of particulate matter are introduced into the atmosphere in the form of manufactured chemicals, refining fossil fuels, mining and smelting ores, quarrying, cement manufacturing, and farming activities.
Sizes of Particulates: Particulates range in size from ultramicroscopic particles, consisting of a few molecules clustered together, to grains of ash, or dust large enough to be seen under a magnifying glass. Small particulates remain suspended almost indefinitely in the atmosphere. They travel freely at the speed of the wind. They can rise to great heights and may enter the stratosphere.
Upward Diffusion of Pollutants: If particulates larger than 1 micron settle continually downward through the air how do they arrive at high level in the first place? The answer lies in atmospheric turbulence and convection. Wind consists of innumerable small eddies, resembling light, corkscrew motion. When the upward air speed is greater than the natural rate of fall of a particle, the particle is lifted. Thus particulates generally diffuse upward into the atmosphere through the same wind flow that also carries them long distances horizontally.
Convection, another mechanism of the rise of particulates, consists of updrafts somewhat like the rise of hot air in a chimney. Many industrial sources, particularly large smokestacks emit hot air that rises rapidly in a column because the air is less dense than its surroundings. In this way many pollutants can be carried up many hundreds of feet before the heat of the rising air column is lost to the surrounding air, halting further rise.