NOx

Nitrogen Oxide and Nitrogen Dioxide, commonly referred to as NOx, are widely regarded to cause health problems and Environmental Impact upon release into the. NO is more readily emmitted to the atmosphere as a primary pollutant, from traffic and power stations, and is often oxidised to the more toxic nitrogen dioxide following dispersal. Road Vehicles are responsible for over 50% of the emissions of nitrogen oxides in the UK. Annual mean concentrations of NO2 in urban areas are generally in the range 10-45ppb. Levels vary significantly throughout the day, with peaks generally occurring twice daily as a consequence of "rush hour" traffic. 
 

Formation of NOx 

Three reaction paths, each with unique characteristics, are responsible for the formation of NOx: Thermal NOx is formed during high temperature processes that result in the combination of atmospheric Nitrogen and Oxygen 
Fuel NOx is formed througfh the oxidation of fuel-bound Nitrogen in motor vehicles, electric utilities, and other industrial, commercial, and residential sources that burn fuels. 
Prompt NOx is formed by the reaction of fuel derived hydrocarbon fragments with atmospheric Nitrogen. 
It is also worth noting that denitrificating bacteria form Oxides of Nitrogen as part of the natural nitrogen cycle. 

Health and Environmental Problems Associated with NOx 

Ground level Ozone or smog is formed when NOx and volatile organic compounds react in the presence of heat and sunlight. Children, asthmatics, and people who work or exercise outside are susceptible to adverse effects such as damage to lung tissue and reduction in lung function. The pollutant is also suspected to have carcenogenic and mutagenic properties. In addition visibility in cities can be impared, and a unsightly red-brown haze may be observed at dusk. 
NOx and sulphur dioxide can react with other substances in the air to form acid rain which can cause deterioration of cars, buildings and historical monuments; and cause lakes and streams to become acidic and unsuitable for numerous species of aquatic life. 
NOx reacts with ammonia, moisture, and other compounds to form nitric acid and related particles. Human health concerns include effects on breathing and the respiratory system, and damage to lung tissue. Small particles penetrate deeply into sensitive parts of the lungs and can cause chronic respiratory disease such as emphysema and bronchitis, also aggravate existing heart disease. 
Water Quality Deterioration can be caused by increased nitrogen loading in receving waters, particularly coastal estuaries. Additional nitrogen may contain a considerable BOD load, causing nitroficating microorganisms to thrive, accelerateing "eutrophication," and “agal bloom” which leads to oxygen depletion and reduces fish populations. 
Nitrous oxide is a greenhouse gas, which accumulates in the upper atmosphere. Some scientists believe the pollutant contributes to the “Greenhouse Effect”