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Oxides of Nitrogen (NOx)
NOx is a term used to refer to two
types of oxides of nitrogen:
nitric oxide (NO) and nitrogen dioxide (NO2). The major source of
NOx are vehicles, power stations & industries. Levels of NOx in
urban areas vary significantly during the day, with peaks generally
occurring with ‘rush hour’ traffics.
Sulfur Dioxide (SO2)
Sulfur dioxide (SO2), a colorless,
reactive gas, is produced during the
burning of sulfur-containing fuels such
as coal and oil, during metal smelting,
and by other industrial processes. Major
sources include power plants and
industrial boilers. Generally, the
highest concentrations of sulfur dioxide
are found near large industrial sources.
Carbon
Monoxide (CO)
Carbon
monoxide (CO) is an odorless, colorless
gas. It forms when the carbon in fuels
does not completely burn. Vehicle
exhaust contributes roughly 60 percent
of all carbon monoxide emissions
nationwide, and up to 95 percent in
cities. Other sources include fuel
combustion in industrial processes and
natural sources such as wildfires.
Carbon
monoxide concentrations typically are
highest during cold weather, because
cold temperatures make combustion less
complete and cause inversions that trap
pollutants low to the ground.
Carbon monoxide is
a gas which slowly oxidises in the
atmosphere to CO2, therefore the main
source of CO is from vehicle.
Ozone (O3)
Ozone is a secondary pollutant; there
are no direct emissions of O3
into the atmosphere.
Ground level ozone (sometimes called
smog) is formed from automobile,
industrial, and other pollutions by
chemical reactions when there is bright
sunshine with high temperatures. Most
ozone in the troposphere (lower
atmosphere) is formed directly by the
action of sunlight on nitrogen
dioxide.
As a result of the various
reactions that take place, O3 tends
to build up downwind of urban centers
where most of the NOx is emitted from vehicles.
Particulate Matter (PM)
Particulate
Matter, called PM, are very small dust
and soot particles. When we talk about
PM, we talk about “PM10”
and “PM2.5”. PM10
is matter that is 10 micrometers in
diameter. That would be about
one-seventh the width of a strand of
human hair. PM2.5
is even smaller - measuring 2.5
micrometers or less.
PM is made
up of a number of components. Soil and
dust particles and certain metals are
emitted directly into the air as PM.
That is it is
a mixture of
coarse and fine organic and
inorganic substances, present in the
atmosphere as both solids and liquids.
The primary
human-caused sources or main sources of
PM include blowing dust from
construction sites and agricultural
activities, as well as combustion
products from solid fuels such as fly
ash (from power plants), carbon black
(from automobiles and diesel engines)
and soot (from fireplaces and wood
stoves). Along the Wasatch Front, the
effects of
PM can be seen as the
thick brownish haze
that gets trapped in the valleys in
winter months when the air is
still.
Volatile Organic Compounds (VOCs)
VOCs include a very wide range of
individual substances, such as
hydrocarbons, halocarbons and
oxygenates. All VOCs are
compounds of carbon and exist as
atmospheric vapours.
In comparison to other pollutants, the
monitoring of VOCs is not yet
well developed. It includes the
measurement of benzene, xylene and
toluene.
Benzene
(C6H6)
Benzene is a volatile organic compound,
i.e. it readily evaporates.
About 80% of human made emissions come
from petrol fuelled
vehicles.
Lead (Pb)
Lead is a bluish or silver-grey soft
metal. In the context of air
pollution, two of its most important
compounds are used as ‘anti
knock’ additives in leaded petrol. The
concentration of lead emitted
has fallen over recent years due to
increasing use of
unleaded petrol
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