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Air pollutants
Acidifying gasses
Acid deposition of sulphur and nitrogen compounds mainly derives from emissions
of SO2, NOX and NH3. The effects of acidification show up in a number of ways,
including defoliation and reduced vitality of trees, declining fish stocks
in acid-sensitive lakes and rivers.
SO2 and NOX can be oxidised into sulphate (SO4--) and nitrate (NO3-) - either
in the atmosphere or after deposition - resulting in the formation of two and
one H+, respectively. NH3 may react with H+ to form ammonium (NH4+) and by
nitrification in soil NH4+ is oxidised to NO3- and H+ are formed.
Weighting the individual substances according to their acidification effect
total emissions in terms of acid equivalents can be calculated as:

where mi is the emission of pollutant i in ton
Mi is the mole weight [ton/Mmole] of pollutant i
The actual effect of the acidifying substances depends on a combination of two
factors: The amount of acid deposition and the natural capacity of the terrestrial
or aquatic ecosystem to counteract the acidification. In areas where the soil
minerals easily weather or have a high chalk content, acid deposition will be
relatively easily neutralised.
Figure 2.1 shows the emission of Danish acidifying gases in terms of acid equivalents.
In 1990 the relative contribution in acid equivalents was almost equal for the
three gases. In 2003 the most important acidification factor in Denmark was ammonia
nitrogen and the relative contributions for SO2, NOX and NH3 were 7 %, 38 % and
55 % respectively. However, regarding long range transport of air pollution SO2
and NOX are still the most important pollutants.
Read more about the acidifying gasses:
- SO2, SULPHUR DIOXIDE
- NOX, NITROGEN OXIDES
- NH3, AMMONIA
Other air pollutants
Read about other air pollutants :
- NMVOC, NON METHANE VOLATILE ORGANIC COMPOUNDS
- CO, CARBON MONOXIDE
- PAH, POLYCYCLIC AROMATIC HYDROCARBONS
- PM, Particulate Matter
Total emissions for 1990 and 2004:
( Kg ) |
As |
Cd |
Cr |
Cu |
Hg |
Ni |
Pb |
Se |
Zn |
1990 |
1504 |
1139 |
6326 |
10253 |
3339 |
25244 |
122074 |
4470 |
35458 |
2004 |
657 |
577 |
1161 |
8447 |
1064 |
9546 |
5254 |
1837 |
23412 |
Reduction in % |
56 |
49 |
82 |
18 |
68 |
62 |
96 |
59 |
34 |
In general the most important sources of heavy metal emissions are combustion
of fossil fuels and waste. The heavy metal emissions have decreased substantially
the last years. The reductions span from 18 % and 96 % for Cu and Pb,
respectively. The reason for the reduced emissions is mainly the increased
use of gas cleaning devices at power and district heating plants (including
waste incineration plants). The large reduction in the Pb emission is
due to a gradual shift towards unleaded gasoline being essential for
catalyst cars.
According to the UNECE Heavy Metal Protocol the priority metals are Pb,
Cd and Hg and the objective is to reduce the emissions of these heavy
metals.
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