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Turbidity – Particles of matter are naturally suspended in water. These
particles can be clay, silt, finely divided organic and inorganic matter, plank-
ton and other microscopic organisms. Turbidity is a measurement of how
light scatters when it is aimed at water and bounces off the suspended parti-
cles. It is not a measurement of the particles themselves. In general terms, the
cloudier the water, the more the light scatters and the higher the turbidity.
The treated water turbidity target is 0.1 NTU (nephelometric turbidity units).
25. Read the text AIR POLLUTION and write a brief summary to the
text.
AIR POLLUTION
Air pollution is the introduction of chemicals, particulate matter, or bio-
logical materials that cause harm or discomfort to humans or other living or-
ganisms, or damages the natural environment, into the atmosphere.
The atmosphere is a complex, dynamic natural gaseous system that is
essential to support life on planet Earth. Stratospheric ozone depletion due to
air pollution has long been recognized as a threat to human health as well as
to the Earth's ecosystems.
An air pollutant is known as a substance in the air that can cause harm to
humans and the environment. Pollutants can be in the form of solid particles,
liquid droplets, or gases. In addition, they may be natural or man-made.[1]
Pollutants can be classified as either primary or secondary. Usually,
primary pollutants are substances directly emitted from a process, such as ash
from a volcanic eruption, the carbon monoxide gas from a motor vehicle ex-
haust or sulfur dioxide released from factories.
Secondary pollutants are not emitted directly. Rather, they form in the
air when primary pollutants react or interact. An important example of a sec-
ondary pollutant is ground level ozone - one of the many secondary pollut-
ants that make up photochemical smog.
Major primary pollutants produced by human activity include:
Sulfur oxides (SOx) – especially sulfur dioxide, a chemical compound
with the formula SO2. SO2 is produced by volcanoes and in various indus-
trial processes. Since coal and petroleum often contain sulfur compounds,
their combustion generates sulfur dioxide. Further oxidation of SO2, usually
in the presence of a catalyst such as NO2, forms H2SO4, and thus acid rain.
This is one of the causes for concern over the environmental impact of the
use of these fuels as power sources.
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