1.   First, the nitrogen oxides are toxic to animals.

2.   Government monitoring stations measure levels of pollutants such as nitrogen oxides or low-level ozone but fail to publicise them widely.

3.   Reduction of nitrogen oxides from cars will need more expensive vehicles - or mean less use.

4.   The nitrogen oxides are almost as effective as dust at screening out sunlight.

5.   Britain agreed to cut emissions of nitrogen oxide from power stations.

6.   For example, nitrogen monoxide, NO, is also called nitrogen oxide.