Environmental Engineering Reference
In-Depth Information
8.3.3.
Atmospheric pollution
To be considered polluting agents, substances have to be present in a sufficient
concentration to have a harmful effect on life and/or materials. Polluting agents in
the atmosphere are in gaseous or particulate state.
Gaseous polluting agents are classified in two categories: those directly emitted
into the atmosphere, for instance SO
2
, called
primary pollutants
, and those
originating from a chemical transformation in the atmosphere, called
secondary
pollutants
, for instance NO
2
originating from the oxidation of NO.
Particles originate from industrial activity (metallic dusts, etc.) and farming
activity (fertilizers, etc.). The atmosphere also contains a number of other natural
terrigenous and biogenic particles.
Gaseous and particulate pollutants have a combined action resulting in soiling,
crust formation and irreversible mineralogical transformations of stone.
8.3.3.1
. Gaseous atmospheric pollution
Gaseous pollution in the atmosphere is composed of different gazes: carbon
monoxide (CO), carbon dioxide (CO
2
), methane (CH
4
), nitrogen oxides (NO and
NO
2
, N
2
O), sulfur dioxide (SO
2
), ozone (O
3
) and chlorofluorocarbons (CFCs).
The most active on stone are nitrogen oxides and sulfur dioxide. These
components may have natural and anthropogenic sources. Natural nitrogen oxides
originate mainly from soils, through the oxidizing action of bacteria on proteins
(11 Mt per year). The natural sources of sulfur are oceans (dimethyl-sulfides),
biogenic earth sources (H
2
S) and volcanoes (SO
2
).
Anthropogenic sources of nitrogenous components are the oxidation of nitrogen
in the air during the combustion of hydrocarbons in engines, domestic heating and
industrial activity (30 Mt per year).
Another source of nitrogenous pollution (NH
3
) is the production of manure by
domestic animals, which is sprayed on fields. This pollution originates from urea in
feces. Sulfurous components linked to human activity originate from coal burning
(60 %), fuel (28%), non-ferrous metal foundries, and factories producing paper pulp
(12%).
8.3.3.1.1. Impact of nitrogenous components
Although nitrogenous components (nitrates) are frequent in the stones of
monuments, their impact on degradation is generally considered to be negligible.
