NDIR
Non-Dispersive Infra Red.

NDUV
Non-Dispersive Ultraviolet.

Nephelometric
A means of measuring turbidity in a sample by passing light through a sample and measuring the amount of light deflected.

Neutralisation
Decreasing the acidity or alkalinity of a substance by adding alkaline or acidic materials, respectively.

Nitric Oxide (NO)
A gas formed by combustion under high temperature and high pressure in an internal combustion engine; changes into nitrogen dioxide in the ambient air and contributes to photochemical smog.

Nitrogen Dioxide (NO2)
The result of nitric oxide combining with oxygen in the atmosphere; major component of photochemical smog.

Nitrogen Oxides (NOx)
Products of combustion from transportation and stationary sources and a major contributor to the formation of ozone in the troposphere and to acid deposition.

Noble Metal
Chemically inactive metal such as gold; does not corrode easily.

Normalisation
A way of expressing a measurement to a standard set of conditions.

Nuclear Winter
Prediction by some scientists that smoke and debris rising from massive fires of a nuclear war could block sunlight for weeks or months, cooling the earth's surface and producing climate changes that could, for example, negatively effect world agricultural and weather patterns.