Urban pollution and air pollutants


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The air and pollutants

The air is the first of the elements necessary for life. Every day we breathe about 14 kg air or 11 000 liters.

The man entered the atmosphere substances with harmful consequences for health and the environment. These substances are emitted by stationary and mobile sources: boilers, industrial, domestic and agricultural, road transport of people and goods ...

The pollutants are dispersed by the wind, dissolved by rain, or blocked when the atmosphere is stable.

The normal chemical composition of the air is nitrogen 78% oxygen 21% argon and other gases 0,9 0,1%

pollutants

The air we breathe can contain hundreds of pollutants in gaseous, liquid or solid. The following pollutants are considered indicators of pollution and are therefore subject to regulation.

The origin of major pollutants

Sulphur dioxide (SO2)

This gas comes mainly from the combination of the sulfur content in fossil fuels (coal, oil, poor quality diesel ...) with oxygen in the air when burned. Industries and heating systems are major emitters.

Nitrogen oxides (NO, NO2)

They result from the reaction of nitrogen and oxygen which occurs at high temperature in engines and combustion plants. Vehicles emit most of the pollution; followed by heating systems.

suspended particles (PM10 and PM2,5)

These are the dust with a diameter less than or 10 2,5 .mu.m .mu.m and which remain suspended in the air. They result from the combustion of wear on vehicles on the roadway and erosion. This dust can also carry other pollutants such as heavy metals and hydrocarbons. Major emitters are diesel vehicles, incinerators, cement plants and certain industries.

The PM2,5 are particularly dangerous because they move faster in the body while PM10 are already more visible but also more easily adopted by mucous membranes.

More: the fine particles

Carbon monoxide (CO)

It results from the incomplete combustion of fuels. In ambient air, it is found mainly near the bus lanes.
Especially from gasoline vehicles: recent cold engine, small engine (eg gardening) and uncatalyzed old vehicles still passing technical inspection.

Volatile organic compounds (VOCs)

They are many, they are mainly oil, whose origin is either natural or due to human activities: road transport, industrial or domestic use of solvents, evaporation of oil storages and reservoirs automobiles, and combustion.

Polycyclic aromatic hydrocarbons (PAHs)

These are compounds whose molecule is cyclical, highly toxic and peristants.
They consist of carbon atoms and hydrogen molecules whose structure comprises at least two fused aromatic rings. They are part of POPs (see below)

"Pyrolytic" PAHs are generated by processes of incomplete combustion of organic matter at high temperatures. The mechanisms involved in their formation involve the production of free radicals by pyrolysis at high temperature (≥ 500 ° C) of the fossil material (oils, fuel oil, organic matter ...) under oxygen deficient conditions. PAHs of pyrolytic origin come from the combustion of automotive fuel, domestic combustion (coal, wood), industrial production (steelworks), energy production (oil or coal-fired power plants, etc.) or still incinerators.

Persistent organic pollutants (POPs)

Persistent organic pollutants (POPs) are a family of pollutant but rather a classification that encompasses several families.
Thus they are molecules defined by the following properties:
- Toxicity: they have one or more proven adverse impacts on human health and the environment.
- Persistence in the environment: they are molecules that are resistant to natural biological degradation.
- Bioaccumulation: the molecules accumulate in living tissue and therefore increase concentrations along the food chain.
- Long-distance transport: by their persistence and bioaccumulation properties, these molecules tend to travel very long distances and deposition of emission sites, typically hot environments (high human activity) to environments cold (especially the Arctic).

Example of POPs: dioxins, furans, PCBs, Chlordécone ...

Metals (Pb, As, Ni, Hg, Cd ...)

This term encompasses all the metals present in the atmosphere. The main having a toxic nature are: lead (Pb), cadmium (Cd), arsenic (As), nickel (Ni), mercury (Hg). In the air, they are found mainly in particulate form. They are mostly from road traffic, the steel industry and waste incinerators.

Ozone (O3)

This gas is the product of the photochemical reaction of certain pollutants, including nitrogen oxides (NOX) and volatile organic compounds (VOCs) under the effect of solar radiation. This pollutant has the distinction of not being emitted by a source; this is a secondary pollutant. It is found mainly in summer, on the outskirts of towns.

The effects of pollution

They are multiple and must be studied case by case! Of all the environments with which man is in contact, the air is the only one he can not escape: it is indeed breathe to live.

The effects of air pollution depend on the amount of pollutant with which the organism is in contact; we speak of "dose". This dose varies depending on 3 factors:

- The concentration of pollutants in the atmosphere,
- The duration of the exhibition,
- The intensity of physical activity,

The disorders occur mainly in susceptible individuals that are:
- Children,
- Old people,
- Asthmatics,
- The respiratory failure,
- Heart,
- Chronic bronchitis,
- Smokers,
- Pregnant women,
- Professionals in contact with chemicals (mechanics, building trades, industry officials ...).

Health Impacts

Depending on the nature of the pollutants, the health consequences are different, even if the various harmful constituents often act synergistically.

The effects on human health of some pollutants

Sulphur dioxide (SO2)

It is an irritant gas. It causes impaired lung function in children and exacerbation of acute respiratory symptoms in adults (cough, difficulty breathing ...).
People with asthma are particularly susceptible.

Nitrogen oxides (NO, NO2)

It is an irritant gas that enters the finer ramifications of the respiratory tract, resulting in bronchial hyperresponsiveness in patients with asthma and increased susceptibility to bronchial infections in children.

suspended particles (PM10)

Larger particles are retained by the upper respiratory tract. They are therefore less harmful to health than the finer particles PM2,5 (then they irritate the lower airways and impair lung function and even, ultimately, cardiovascular.

Some, by nature, also have mutagenic and carcinogenic properties.

Carbon monoxide (CO)

deadly gas. It attaches instead of oxygen on blood hemoglobin leading to lack of oxygenation of the nervous system, heart and blood vessels. The central nervous system and sensory organs are affected first, causing headache, dizziness, asthenia or sensory disturbances. If very high and prolonged exposure, it can be fatal or leave irreversible neuropsychological sequelae.

Volatile Organic Compounds (VOCs) including benzene

These molecules have very different effects depending on family. From simple discomfort olfactory (smell), some cause irritation (aldehydes) or a decrease in breathing capacity. Others, such as benzene, cause mutagenic and carcinogenic effects.

Metals (Pb, As, Ni, Hg, Cd ...)

These different elements accumulate in the body, resulting in a long-term toxicity risk involving possible carcinogenic properties.

Ozone (O3)

This gas, highly oxidizing, easily penetrates to the finer airways. It causes coughing and lung damage, especially in children and asthma, and eye irritation.

Environmental impact

A long-term environmental effects can occur at lower concentrations than those harmful to humans.

The most visible consequences are often blackening of buildings and monuments, including the cost of restoration is often very heavy.
Nitrogen oxides and sulfur dioxide contribute significantly to acid rains which destroy the environment and the building materials.

The most oxidizing pollutants (ozone) reduce plant photosynthetic activity, which results in a visible manner by smearing (necrosis) on the leaf surface of the plants more susceptible. This leads to growth slowdowns in plants. agricultural yield reductions were even observed.

The influence of weather on pollution

The pollutants are dispersed by the wind, dissolved by rain or blocked when the atmosphere is stable.

Thus, the anticyclonic periods characterized by calm weather with low wind, sometimes with a temperature inversion in winter, contribute to a rapid increase in the concentration of pollutants at ground level.
Under normal conditions, the air temperature decreases with altitude. The hot air containing pollutants tends to rise naturally. The pollutants disperse vertically.

In the event of a temperature inversion, the soil has cooled significantly during the night (for example, winter in clear weather). The temperature at a few hundred meters altitude is then higher than that measured at ground level. The pollutants are thus locked under a "cover" of hot air, called the inversion layer.

The SFX index

SFX The index was designed on the initiative of the Ministry of Spatial Planning and the Environment, in order to qualify the air quality of a homogenous urban unit.



This index is representative of urban air pollution background conurbation, felt by the majority of its inhabitants. It is calculated on a day (0 24 am to h). To promptly notify a partial index is calculated in the afternoon with the measured values ​​up to 16 hours.

It does not help to highlight particular phenomena or localized pollution, proximity example. It is a synthetic figure of the status of the air associated with a qualifier:

very good 1
very good 2
3 bon
4 bon
Means 5
poor 6
poor 7
8 bad
9 bad
10 bad

Four pollutants are used to construct the index SFX: sulfur dioxide (SO2), nitrogen dioxide (NO2), ozone (O3) and suspended particles (PM10).

These chemical species are considered as indicators of air pollution.

For each of these pollutants, a sub-index is determined by reference to a correlation table where each concentration range is assigned a value. The final index is the sub-index is the largest.

Example of measures:
Subindex SO2 = 1
Subindex PM10 = 2
Subindex O3 = 5
Subindex NO2 = 2
SFX index = 5

More details

- The dead of pollution in France
- urban and alternative transport Study on pollution


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