Nitric oxide (also known as nitrogen monoxide) is a chemical compound with the chemical formula NO. This diatomic molecule is a free radical. This gas is an important intermediate in the chemical industry. Nitric oxide is an air pollutant produced by combustion of substances in air, like in automobile engines and fossil fuel power plants.  In mammals including humans, NO is an important cellular signaling molecule involved in many physiological and pathological processes. Low levels of NO production are important in protecting an organ such as the liver from ischemic damage. Chronic expression of NO is associated with various carcinomas and inflammatory conditions including juvenile diabetes, multiple sclerosis, arthritis and ulcerative colitis.

Nitric oxide should not be confused with nitrous oxide (N2O), an anesthetic and greenhouse gas, or with nitrogen dioxide (NO2), a brown toxic gas and a major air pollutant. However, nitric oxide is rapidly oxidized in air to nitrogen dioxide (source Wikipedia).

<strong>Method Of Production</strong>
In 1746 in Birmingham, England, John Roebuck began producing sulfuric acid in lead-lined chambers, which were stronger, less expensive, and could be made much larger than the glass containers which had been used previously. This allowed the effective industrialization of sulfuric acid production and with several refinements, this process remained the standard method of production for almost two centuries. So robust was the process that as late as 1946, the chamber process accounted for 25% of sulfuric acid manufactured. Sulfur dioxide is introduced along with steam and oxides of nitrogen into large chambers lined with sheet lead where the gases are sprayed down with water and chamber acid. The sulfur dioxide and nitrogen dioxide dissolve and over a period of a approximately 30 minutes, the sulfur dioxide oxidized to sulfuric acid. The presence of nitrogen dioxide is necessary for the reaction to proceed. The process is highly exothermic, and a major consideration of the design of the chambers was to provide a way to dissipate the heat formed in the reactions. Early plants used very large wooden rectangular chambers (Faulding box chambers) that were cooled by ambient air. Around the turn of the nineteenth century, such plants required about half a cubic meter of volume to process the sulfur dioxide equivalent of a kilogram of burned sulfur. In the mid 19th century, French chemist Gay-Lussac redesigned the chambers as stoneware packed masonry cylinders. In the 20th century, plants using externally cooled Mills-Packard chambers supplanted the earlier designs.

Sulfur dioxide for the process can be provided by burning elemental sulfur or by the  roasting of sulfur containing metal ores in a stream of air in a furnace. During the early period of manufacture, nitrogen oxides were produced by the decomposition of niter at high temperature in the presence of acid, but this process was gradually supplanted by the air oxidation of ammonia to nitric oxide in the presence of a catalyst. The recovery and reuse of oxides of nitrogen was an important economic consideration in the operation of a chamber process plant.
In the reaction chambers, nitric oxide reacts with oxygen to produce nitrogen dioxide. Liquor from the bottom of the chambers is diluted and pumped to the top of the chamber and sprayed downwards in a fine mist. Sulfur dioxide and nitrogen dioxide are absorbed in the liquid and react to form sulfuric acid and nitric oxide. The liberated nitric oxide is sparingly soluble in water and returns to the gas in the chamber where it reacts with oxygen in the air to reform nitrogen dioxide. Some percentage of the nitrogen oxides are sequestered in the reaction liquor as nitrosylsulfuric acid and as nitric acid, so fresh nitric oxide must be added as the process proceeds. Later versions of chamber plants included a high temperature Glover tower to recover the nitrogen oxides from the chamber liquor, while concentrating the chamber acid to as much as 78% H2SO4. Exhaust gases from the chambers are scrubbed by passing into a tower through which some of the Glover acid flows over broken tile. Nitrogen oxides are absorbed to form nitrosylsulfuric acid which is then returned to the Glover tower to reclaim the oxides of nitrogen. Sulfuric acid produced in the reaction chambers is limited to about 35% concentration. At higher concentrations, nitrosylsulfuric acid precipitates on the lead walls as chamber crystals and is no longer able to catalyze the oxidation reactions (source Wikipedia).

<strong>Nitrogen Oxide Environmental Problems</strong>
The following environmental problems may arise from Nitrogen Oxide pollution:

1. Contributes to global warming
2. Hampers the growth of plants
3. May form with other pollutants to form toxic chemicals
4. Helps form acid rain

<strong>Nitrogen Oxide Effect On Humans</strong>
Nitrogen Oxide may have the following effects on humans:

1. Nitrogen Oxide, plus other ground-level ozone, can cause major respiratory problems in high levels
2. Breathing in high levels of Nitrogen Oxide can lead to: rapid burning spasms; swelling of throat; reduced oxygen intake; a larger buildup of fluids in lungs and/or death
3. Visual impairment in the areas affected by Nitrogen Oxide
4. Small levels of Nitrogen Oxide can cause nausea, irritated eyes and/or nose, fluid forming in lungs and shortness of breath
5. Can react with aerosols from aerosol cans and can also cause respiratory problems

<strong>Steps To Minimize Risk Of Nitrogen Oxide Pollution</strong>
The following steps may be taken to minimize the risk of Nitrogen Oxide Pollution:

1. Not smoking cigarettes
2. Reduce exposure to silos that contain silage
3. Not living in large rural area, or near an industrial part of town
4. Avoid high industrialized areas

In conclusion, the best way of being free from the hazard produced by carbon monoxide, the world must seek alternative energy sources.

<strong>Resources</strong>
The following are resources for more information on Nitric Oxide:

1. Wikipedia - <a title="Nitric Oxide" href="http://en.wikipedia.org/wiki/Nitric_Oxide" target="_blank">Nitric Oxide</a>
2. Perpetual Minds - The Greenhouse Effect

Image Credit: <a title="Wikipedia" href="http://en.wikipedia.org/wiki/File:Nitric-oxide-3D-vdW.png" target="_blank">Wikipedia</a>