Page 34 - Curriculum Visions Dynamic Book

NOx
The three important gases of nitrogen, nitrogen dioxide, nitrous oxide and nitric oxide, are collectively referred to as NOx (pronounced “nox”).
Nitrous oxide, or laughing gas, is a colourless gas. When it is inhaled, nitrous oxide makes people feel intoxicated (hence the tendency to laugh). It also makes people lose the sensation of pain and then makes them unconscious.
Its effects do not last very long. This is
why it is used in dental and other minor operations.
Nitrous oxide dissolves in fatty liquids such as cream. So can be used as the inert propellant in foamed cream.
Nitric oxide is far less pleasant, a colourless gas that reacts on contact with oxygen in the air to produce the brown gas nitrogen dioxide. Nitric oxide is
often produced at high temperature and pressure. One of the most common places for this reaction is inside the cylinder of
a motor vehicle.
Nitrogen dioxide can damage the breathing passages of the lungs. The damage often goes undetected until
days after the gas is inhaled, when it may cause excessive fluid build-up in the lungs.
Nitrogen dioxide is also an important contributor to the production of ozone, which itself has harmful effects. Nitrogen dioxide also contributes to the formation of nitrate particles, another part of smog.
 Smog over Los Angeles, California, USA.
Controlling NOx emissions
It is very difficult to prevent NOx gases from leaving the exhausts of vehicles, because they are a natural product of internal combustion. Some catalysts can reduce nitric oxide emissions by making nitric oxide oxidise carbon monoxide, producing inert nitrogen, carbon dioxide, and water. However, the catalytic converter in modern vehicles is extremely expensive.
Also... Smog
Smog is a mixture of gases and small particles suspended in the air. The gases come from power station, factory and vehicle exhausts. The main gas produced is nitrogen dioxide, which is responsible for the brown haze that occurs in the sky over many cities. Local visibility is reduced not by the gases, but by small particles in the air, some of them dust and carbon particles, some of them formed
as the nitrogen and sulphur gases react to produce sulphates and nitrates.
34
34