86 AIR POLLUTION SOURCES
Part 1. Pollutant Emissions (continued)Pollutant types Sources and abundance Abatement and control
b. Hydrogen Sulfide: Hydrogen sulfide (H 2 S) is a colorless gas
known by its characteristic rotten egg odor.
Natural sources of H 2 S include volcanic
eruptions, geothermal wells and chemical
or bacteriological decomposition of mineral
sulfates in springs and lakes. In these natural
occurances, other sulfur compounds are nearly
always present with the H 2 S.
Anthropogenic sources include the combustion of
coal, natural gas and oil. The refining of
petroleum products, coke production, sulfur
recovery operations and the kraft process for
producing chemical pulp from wood are all
major sources of H 2 S.
The typical rotten egg odor can be detected at very
low concentrations, 0.025 to 0.2 ppm, but at these
concentrations it has little or no effect upon
human health. However, at higher concentrations,
H 2 S is extremely toxic. Above 150 ppm, the
human olfactory apparatus becomes paralyzed,
effectively preventing any olfactory warning
signal. H 2 S is life threatening at 300 ppm since it
causes pulmonary edema. At 500 ppm, there is
strong stimulation to the nervous system. Above
1000 ppm, there is immediate collapse and
respiratory paralysis.Most removal system for H 2 S scrub the
gas streams with a suitable absorbent
and then remove the absorbed gas
from the absorbent for disposal by
burning or conversion to usable by-
products. Different types of scrubbers
can be used such as spray towers,
plate towers and venturi scrubbers.
Natural removal of H 2 S occurs by
atmospheric conversion to SO 2 which
is subsequently removed from the
atmosphere through precipitation and
absorption by surfaces and vegetation.- Nitrogen Compounds: There are five major
gaseous forms of nitrogen in the atmosphere:
nitrogen gas (N 2 ), ammonia (NH 3 ), nitrous oxide
(N 3 O), nitric oxide (NO), and nitrogen dioxide
(NO 2 ). N 2 is the major gaseous component in the
atmosphere and counts for 78% of the
atmosphere’s mass. NO and NO 2 are important
pollutants of the lower atmosphere and because
of their interconvertibility in photochemical
reactions, are usually collectively grouped as
NOx.
Nitrous oxide (N 2 O) is a colorless, slightly sweet,
non-toxic gas. It is probably best known as the
“laughing gas” which is widely used as an
anesthetic in medicine and dentistry. Bacterial
action which produces N 2 O is the largest single
source of any nitrogen oxide on a worldwide
basis. It is present in the atmosphere at an
average concentration of 0.27 ppm. It is quite
inert in the lower atmosphere, but it can react
with oxygen atoms that are available in the
stratosphere to produce nitric oxide.
a. Nitrous Oxide:
b. Nitric Oxide: Nitric oxide (NO) is a colorless, odorless, tasteless,
relatively non-toxic gas. Natural sources include
anaerobic biological processes in soil and water,
combustion processes and photochemical
destruction of nitrogen compounds in the
stratosphere. On a worldwide basis, natural
emissions of NO are estimated at approximately
5 108 tons per year. Major anthropogenic
sources include automobile exhaust, fossil fuel
fired electric generating stations, industrial
boilers, incinerators, and home space heaters.
All of these sources are high temperature
combustion processes which follow the reaction:
N 2 O 2 2NO (6)
This reaction is endothermic, which means that
the equilibrium shifts to the right at
high temperatures and to the left at low
temperatures. Therefore, as the combustion
temperature of a process increases, so will the
amount of CO emitted.
Background concentrations of NO are
approximately 0.5 ppb. In urban areas, one hour
average concentrations of NO may reach 1 to 2
ppm. Atmospheric levels of CO are related to the
transportation and work cycle, with the highest
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