Problems caused as a consequence of accumulation of aerosols in the atmosphere are of diverse nature which depend chiefly on the size of particles, their chemical nature, whether toxic or nontoxic and whether the particles are viable or non-viable. These problems can be summarized as follows:
1. A dense layer of aerosols in the atmosphere blocks a considerable portion of solar radiations. As sun’s rays are checked high up in the atmosphere, earth’s temperatures are lowered which may at times disturb local weather conditions, pressure patterns and precipitation. The photosynthetic efficiency of green vegetation of the area thus involved may also be affected. A large-scale nuclear war, for example, shall form such a dense envelop of particulate material around the globe that temperatures shall drop to sub-zero-levels.
2. Aerosols provide a suitable nucleus or locus on which vapours in the atmosphere condense and this accelerates precipitation. Likewise fine particulate material or aerosols provide suitable loci for various atmospheric chemical reactions to occur. It is on these particles that water forms a fine film which dissolves or adsorbs various contaminants present in the atmosphere which react with each other.
When two or more than two aerosols come together and fuse larger and heavier particles are formed while their contents react together. The metallic constituent of the aerosols acts as catalytic agent for these reactions. The secondary aerosols thus developed are heavier and bear various reactants and reaction products of the atmospheric reactions.
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They are like a condensed package of the chemical contents of the atmosphere. Being heavier they tend to drift down and cause dry precipitation. The entire aerosol content of the atmosphere may be brought down by rains, dew or snow. Thus acid rains, fog or smog, oxidizing type of pollution etc. are caused.
3. Air currents are able to disperse aerosols far and wide. Thus aerosols composed of toxic metals and trace elements are also transported to great distances and deposited at places far removed from the place of their origin. For example, fly-ash which contributes about 0.01 -0.3% of the toxic metal content of particulate material in the air may be carried too far off places and deposited there along with rains, snow or dew.
A small rise in the concentration of these elements may appear insignificant. However, innumerable instances of their bio-accumulation, bio-magnification and synergistic action where more than one such element are involved are on the record. Therefore, even small rise in the concentration of heavy metals may lead to serious consequences.
4. Viable particulate material in the atmosphere is responsible for the dissemination of many pathogenic diseases and allergenic agents of various types. Fungi like Alternaria, Aspergillus, Fusarium, Penicillium, Helminthosporiuin etc. are dispersed by air currents so also are many bacteria and viruses (such as viruses causing conjectivitis or flu virus). Pollen grains and other viable material like algae and fungi are often responsible for causing various allergenic disorders in susceptible individuals.
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5. These fine particles are capable of penetrating deep inside the lungs of organisms and cause various respiratory ailments. Some of the aerosols are potential carcinogenic agents. Inhalation of these particles irritates lungs and exposure for long duration’s causes scarring or fibrosis in the alveolar lining.