causes
There are many substances in the air which may impair
the health of plants and animals (including humans), or reduce visibility.
These arise both from natural processes and human activity. Substances
not naturally found in the air or at greater concentrations or in different
locations from usual are referred to as pollutants.
Major primary pollutants produced by human activity include:
• Sulfur oxides (SOx) especially sulfur dioxide are emitted from burning
of coal and oil.
• Carbon monoxide is colorless, odorless, non-irritating
but very poisonous gas. It is a product by incomplete combustion of
fuel such as natural gas, coal or wood. Vehicular exhaust is a major
source of carbon monoxide.
• Carbon dioxide (CO2), a greenhouse gas emitted from combustion.
• Toxic metals, such as lead, cadmium and copper.
• Ammonia (NH3) emitted from agricultural processes.
• Odors, such as from garbage, sewage, and industrial processes
• Radioactive pollutants produced by nuclear explosions and natural
processes such as radon.
Secondary pollutants include:
• Particulate matter formed from gaseous primary pollutants and compounds
in photochemical smog, such as nitrogen dioxide.
• Ground level ozone (O3) formed from NOx and VOCs.
Minor air pollutants include:
• A large number of minor hazardous air pollutants.
• A variety of persistent organic pollutants, which can attach to particulate
matter.
