Range of air pollutant levels
THE Observer Air Index has registered FAIR a number of times over the past month with many enquiries asking what it means.
The air quality monitors register a number of pollutants that raise the level monitor. Owing to major industrial projects a lot of earthworks are stirring up dust, which does register in the data.
The air quality index is calculated by converting the measured pollutant concentrations into index values. To generate these values, pollutant concentrations are expressed as a proportion of the air standards and then categorised according to that value.
The five categories in the department's Air Quality Index, ranging from Very Poor to Very Good are defined by index value ranges below: Very Good 0–33%, Good 34% –66%, Fair 67%–99%, Poor 100%–149%, Very Poor – 150%.
So an index of Fair means that the concentration of one of the contaminants measured at that site was between 67% and 99% of the associated guideline. The recent events when air quality was Fair were associated with strong winds raising concentrations.