Air Pollutants: Gases and Their Effects

When nitrogen is released, it combines with oxygen and becomes NO, later it combines with oxygen to become $NO _2$. It causes       of lungs, lowers the resistance to respiratory infection. If level increases it causes intense astama on people. Because air pollution is more in urban than in rural areas,  lung diseases are more probable in urban areas.

Tropospheric pollution is caused by gaseous pollutant and particulate matter. Some of the gaseous air pollutant are hydrogen sulphide, oxides of sulphur, oxides of nitrogen etc.

Hydrogen sulfide gas is a naturally occuring chemical. The gas has a characteristic rotten egg odor at low concentrations. About half of the population can smell it at concentrations as low as 8 parts per billion (ppb) in air, and more than 90% can smell it at levels of 50 ppb.  At higher concentrations, hydrogen sulfide rapidly deadens the sense of smell.

Hydrocarbon is produced as a result of incomplete combustion of fuels in automobile engines.
In animals, hydrocarbons can cause cancer, while in plants, they cause ageing by breaking down tissues, which causes shedding of leaves, twigs and flowers.

Lead is one of the major pollutant which is released from lead batteries, industries etc. It damages kidney, liver, brain and central nervous system.

Hydrogen sulfide gas is found in petroleum and natural gas. Oil or natural gas is considered sour if it has a high percentage of hydrogen sulfide. Natural gas can contain up to 28 percent hydrogen sulfide gas, consequently,  it may be an air pollutant near petroleum refineries and in oil and gas extraction areas.

Brown ring compound $FeSO _4.NO$

Air pollution from cars and trucks is split into primary and secondary pollution. Primary pollution is emitted directly into the atmosphere; secondary pollution results from chemical reactions between pollutants in the atmosphere. The following are the major pollutants from motor vehicles:

1. Photochemical smog is composed of primary and secondary pollutants.
2. Primary pollutants, which include nitrogen oxides and volatile organic compounds are introduced into the atmosphere via vehicular emissions and industrial processes.
3. Secondary pollutants, like ozone, result from the reaction of primary pollutants with ultraviolet light.

Nowadays, the mixture of particulates with gaseous oxides of sulphur present in the atmosphere is called classical smog. The principal source of classical smog is the combustion of industrial and household fuels (coal and petroleum). Because of the presence of $S{ O } _{ 2 }$ and carbon (soot) particles, classical smog has a reducing character. It occurs in winter months, particularly in early morning hours. It causes severe lung and throat irritation.

The reaction of sunlight with hydrocarbons and ${ NO } _{ 2 }$ results in a variety of chemical products. One of these is ozone, made up of 3 atoms of oxygen, which is an irritating noxious gas. Other undesirable chemicals such as aldehydes also result from this photochemical reaction. This type of smog is oxidizing in character because of the presence of ozone, nitrogen dioxide, and some photochemical oxidants.

The reaction of sunlight with hydrocarbons and ${ NO } _{ 2 }$ results in a variety of chemical products. One of these is ozone, made up of 3 atoms of oxygen,which is an irritating noxious gas. Other undesirable chemicals such as aldehydes also result from this photochemical reaction. This type of smog is oxidizing in character because of the presence of ozone,nitrogen dioxide and some photochemical oxidants.

Acute harm due $N{ O } _{ 2 }$ exposure is only likely to arise in occupational settings. Direct exposure to the skin can cause irritations and burns. Only very high concentrations of the gaseous form cause immediate distress: 10–20 ppm can cause mild irritation of the nose and throat, 25–50 ppm can cause edema leading to bronchitis or pneumonia, and levels above 100 ppm can cause death due to asphyxiation from fluid in the lungs. There are often no symptoms at the time of exposure other than transient cough, fatigue or nausea, but over hours inflammation in the lungs causes edema.

1. When exposed to oxygen, ntric oxide is converted into nitrogen dioxide  $2NO+{ O } _{ 2 }→2N{ O } _{ 2 }$
2.  Nitrogen dioxide , a brown toxic gas and a major air pollutant.
   

NO binds rapidly to haem iron in Hb and once bound, the NO activity is largely irretrievable, the binding is purportedly so tight as to be unaffected by ${ O } _{ 2 }$ or CO. So, NO has the greatest affinity toward haemoglobin. 

Of the $N{ O } _{ x }$  absorbed by acid, typically less than 10% enters the large flow of acid circulating around the acid towers. Instead, it concentrates on the much smaller quantity of acid mist formed at the inlet to the absorber towers. There are several reactions involved, but the net result can be summarised as: 

The gaseous pollutants of the atmosphere are harmful gaseous oxides and oxidants. The harmful gaseous oxides include the oxides of sulphur, nitrogen, and carbon, besides hydrocarbons.

Sources of lead emissions vary from one area to another. At the national level, major sources of lead in the air are ore and metals processing and piston-engine aircraft operating on leaded aviation fuel. Other sources are waste incinerators, utilities, and lead-acid battery manufacturers. The highest air concentrations of lead are usually found near lead smelters.

Agriculture is by far the biggest source of ammonia emissions. Livestock farming and animal waste account for the biggest percentage of total ammonia emissions which are due to the decomposition of urea from large animal wastes and uric acid from poultry wastes.

The most common pollutant of nitrogen gas is nitrogen dioxide, is produced when fossil fuels are burnt in high temperature like in automobile engines.

Dinitrogen and dioxygen are the main constituents of air, and they form nitric oxide and nitrogen dioxide in high temperature. Nitric oxide also reacts with the ozone in the earths atmosphere to form nitrogen dioxide.

Hydrogen sulfide is the chemical compound with the formula $H _2S$. It is a colorless chalcogen hydride gas with the characteristic foul odor of rotten eggs. It is very poisonous, corrosive, and flammable.

$H _2S$ gas burns producing toxic gases such as $SO _2$. $H _2S$ is flammable, hence combustible.

Above 100 ppm we can lose the rotten smell of hydrogen sulphide.

$H _2S$ being toxic causes a wide range of health hazards such as nausea, tearing of eyes, headache or loss of sleep or bronchial problems in some asthma patients; acute exposure causes rapid unconsciousness,' knockdown ' or immediate collapse, death within minutes.

Cyanide (CN-) is toxic because it binds with high affinity to the iron atom in the heme group of cytochrome c oxidase, inhibiting the electron transport chain.

$500$ ppm of $H _2S$ can cause staggering and collapse in $5$ minutes. 

$H _2S$ has high risk of health hazards; such as nausea, hearing of eyes, headache or loss of sleep or bronchial problem in some asthama patients; acute exposure causes rapid unconsciousness, 'knockdown' or immediate collapse, death within minutes. 

Hydrogen cyanide $(HCN)$, sometimes called prussic acid, is a chemical compound with the chemical formula $HCN$. 

Lead's four stable isotopes each have 82 protons, a magic number in the nuclear shell model of atomic nuclei. The isotope lead-208 also has 126 neutrons, another magic number, and is hence double magic, a property that grants it enhanced stability: lead-208 is the heaviest known stable nuclide.

Almost all organ systems are affected by hydrogen sulfide, but the most susceptible are those with exposed mucous membranes (e.g., eyes,  noise and throat) and those with high oxygen demands (e.g., lungs, brain).

  At higher concentrations, hydrogen sulfide rapidly deadens the sense of smell which means the ability to sense the smell of anything will be no more at such high temperature.  For most people, this occurs at approximately $150ppm$. The gas has a characteristic rotten egg odour at low concentrations. About half of the population can smell it at concentrations as low as 8 parts per billion ($ppb$) in the air.

Hydrogen sulfide is the chemical compound with the formula $H _2S$. It is a colorless gas with the characteristic foul odor of rotten eggs; it is heavier than air, very poisonous, corrosive, flammable, and explosive.

$2H _2S+3O _2\longrightarrow \underbrace {2SO _2} _{sulphur\quad dioxide}+\underbrace {2H _2O} _{water}$

Exposure to $H _2S$ causes eye irritation thereby causes tearing of eyes. 

Because of its high reactivity toward glass and moderate reactivity toward many metals, hydrofluoric acid is usually stored in plastic containers (although PTFE is slightly permeable to it).

For hydrogen sulfide, it is allowable for workers to be exposed to concentrations of 10 parts per million, averaged over an eight-hour work shift, with the exposure not exceeding 15 parts per million. 
1000ppm and 2000ppm have high probability of death and lose consciousness.

Lead is a neurotoxin that accumulates both in soft tissues and the bones, damaging the nervous system and causing brain disorders.

Ammonia is the simplest pnictogen hydride. N group elements are called pnictogens. And the smallest of all pnictogens is nitogen. So simplest pnictogen hydride is ammonia.

The toxicity of ammonia solutions does not usually cause problems for humans and other mammals, as a specific mechanism exists to prevent its build-up in the bloodstream. Ammonia is converted to carbamoyl phosphate by the enzyme carbamoyl phosphate synthetase, and then enters the urea cycle to be either incorporated into amino acids or excreted in the urine. Fish and amphibians lack this mechanism, as they can usually eliminate ammonia from their bodies by direct excretion. Hence ammonia even in dilute solutions is very harmful for aquatic organisms.

Ammonia is the liquid by-product of production of coke from coal.