Environmental Engineering Reference
In-Depth Information
In polar regions, especially Antarctica, gaseous chlorine nitrate gets trapped in stratospheric
clouds at temperatures below −70°C and during winter time undergoes the following
reactions:
ClONO
+
H O
→ +
HOCl
HNO
[8.13]
2
2
3
ClONO
+→+
HCl
Cl
HNO
[8.14]
2
2
3
HOCl and Cl
2
accumulates on the surface of ice crystals during the dark winter and as soon
as sunlight resurfaces in early spring HOCl and Cl
2
molecules are broken into Cl
•
as follows:
•
Cl
+
light
→
2Cl
[8.15]
2
•
•
HOCl
+
light
→+
HO
Cl
[8.16]
Subsequently, Cl
•
atoms react with ozone according to equation 8.8, which starts the destruc-
tive process of ozone. This phenomenon explains depletions of up to 50 percent of stratospheric
ozone over Antarctica during early spring time (Baird and Cann, 2005; Manahan, 2000).
International treaties have gradually phased out the production and use of chlorofluorocar-
bons and bromofluorocarbons and replaced them with a new family of chemical compounds
that contain only fluorine, hydrofluorocarbons, that do not harm the ozone layer. However,
later it was found that these gases have high GWPs (see Table 8.4).
For a full discussion of stratospheric ozone destruction, consult the Scientific Assessment
of Ozone Depletion by the World Meteorological Association (WMA, 2006).
EMISSIONS INVENTORIES
An emissions inventory is an assessment of the amount of pollutants released to the atmos-
phere over a specific period of time by an organization, a country, or the whole world. Emission
inventories have been used in many countries to report the emission of common air pollutants,
such as sulfur dioxide, nitrogen oxides, particle matter, heavy metals, persistent organic pol-
lutants, and VOCs, to regulatory agencies. More recently, entities have been starting to use
emission inventories to report the emissions of GHGs.
Emissions inventories are based on emission factors. An emission factor is “a representative
value that attempts to relate the quantity of a pollutant (or substance of interest) released to
the atmosphere with an activity associated with the release of that pollutant. These factors
are usually expressed as the weight of pollutant divided by a unit weight, volume, distance, or
duration of the activity emitting the pollutant” (EPA, 1995). The amount of the emission for a
particular pollutant can be calculated as:
Emission
=
Emission Factor
× Activity Rate
[8.17]
(i)
(i)
Where:
Emission
(i)
= Amount of the emission in metric tons or pounds for a particular pollutant, i;
Emission Factor
(i)
= Amount of the pollutant, i, produced for each unit of activity rate (e.g.,
pound of NOx per gallon of fuel burned); and
Activity Rate = Quantity of the activity (e.g., gallons of fuel burned, or ft
3
of natural gas used).
