In June 1998, there were two major changes in relation to air quality and how it is reported:
- national standards were set for how air quality is measured (using six criteria air pollutants)
- national reporting process was introduced.
The six criteria pollutants measured to assess national standards are ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, particles as PM10 and particles as PM2.5 and lead.
In 2002, the then Environment Protection Authority began reporting on these pollutants to the national body. In 2006, the then OEH stopped monitoring lead as levels became undetectable.
The old Regional Pollution Index (RPI) was replaced by an Air Quality Index (AQI) in 2008 based on the five criteria pollutants (as per national standards) plus visibility (as per a standard set by the then NSW Office of Environment and Heritage) at all sites in the air quality monitoring network. NOTE: All indexes for air quality data collected prior to 2008 were recalculated using the new AQI and are now reported in this format.
In 1993, following a major review of monitoring needs, the NSW Government upgraded the monitoring network and extended it to the lower Hunter, Illawarra and western area of Sydney.
As a consequence of the expansion of the network, daily reporting of air quality was also reviewed, resulting in the reporting of a Regional Pollution Index (RPI). The RPI was produced for three regions in Sydney (Eastern Sydney, North Western Sydney and South Western Sydney) three sites in the lower Hunter (Newcastle, Wallsend and Beresfield) and three sites in the Illawarra (Wollongong, Kembla Grange and Albion Park).
Sydney's air has been monitored for a range of pollutants since the 1960s. By the early 1980s, daily air quality reports were being released, based specifically on concentrations of ozone and fine particles. These Sydney Pollution Index (SPI) reports used a simple linear scale that reported pollution levels as low, medium or high. The SPI measured ozone and fine particles from 6am to 3pm. This reflected an emphasis on visible pollution and focused on daytime visibility as a measure of air quality.
At that time Sydney's population lived mainly east of Parramatta and in the south-western areas of Liverpool/Campbelltown. Monitoring was therefore concentrated in these areas.