Oxides of Nitrogen

Why are NOx bad?

It threatens human and environmental health worldwide

Anthropogenic sources

The reaction of N and O₂ in hot combustion processes, for example:

• Vehicular emission sources due to the combustion of petroleum fuels (like diesel)

Are NOx produced by fuel combustion itself?

No

How are NOx formed?

Nitrogen and oxygen from the air are drawn into the engine, and then react with each other under the high temperature and pressure conditions in the engine.

What happens to NO₂ in the presence of sunlight and other hydrocarbon vapours?

More toxic secondary pollutants can be produced, e.g. Peroxyacetyl Nitrates

Where are NOx levels high?

Urban areas

Why do they have high NOx levels?

In urban areas, there are high levels of vehicular traffic and slow moving congestion or stop and go traffic, which reduces the fuel efficiency of vehicles

Fertiliser as a source

NOx release due to nitrogen based fertiliser use.

Effects

• Photochemical smogs.

• Global climate change.

Controls

• Catalytic converters.

• Urea sprays.

• Control of fertilizer use.

Catalytic Converters

• A chamber in the exhaust pipes contain a catalyst (such as platinum)

• The catalyst chemically reduces NOx back to nitrogen and oxygen gases

Urea Sprays

NOx can be removed by reacting it with urea.

It forms N_{2 (g)}, CO₂, and H₂O.

Control of fertiliser use

• Use alternate fertilisers

• Use organic fertilisers like manure and sewage. They have a better C:N ratio