The Council measures both the emissions (discharge monitoring) and the concentrations of various gases downwind of particular sources (ambient monitoring). The Resource Management Act 1991 is concerned with the effects of discharges.
It is sometimes easier and cheaper to measure concentrations of contaminants downwind, because this directly shows what people and the environment are being exposed to.
However, because the area on the ground that is affected by the plume from a discharge stack or vent moves around as the wind swirls and varies, it is sometimes easier to measure a concentration in a discharge and calculate the likely levels downwind at various points.
Gases that the Council has monitored for or required information about include nitrogen oxides, sulphur oxides, formaldehyde, methanol, vinyl chloride, benzene, toluene, xylene, and phenol. Respirable and total suspended dust are also measured from time to time.
One unusual situation was when the Council participated in monitoring the effects of Mt Ruapehu's eruptions in 1996-1997, by sampling Taranaki's air for sulphur oxide levels.