Numbers of high and moderate pollution days across the Sydney area were greater in number in the early and mid 1980s than in the late 1980s and early 1990s. The New South Wales Environment Protection agency (EPA) thought this was caused by a decrease in pollutants emitted due to more stringent emission controls. However, an examination of forecast pollution potential showed a similar decrease. The question therefore arose as to what extent the observed pollution decrease was a function of the synoptic situations and whether there were any identifiable long-term changes in these synoptic patterns. Among the results are included:
1. Identification of the main synoptic situations covering the eastern Australian region associated with moderate to high pollution events in Sydney. The major contributors were those synoptic situations which resulted in a light to moderate north-westerly airstream over the Sydney region. Charts are presented showing synoptic situations which lead to significant pollution events.
2. Possible reasons why pollution events lessened during the late 1980s and early 90s.
3. Relationships between number of pollution days and the amount of time anticyclones are located in a region (anticyclonicity). Maps are presented showing anticyclonicity anomalies for 4 months (one for each season), for which a large number of pollution days were registered. Correlations between anticyclonicity with moderate and high pollution registrations for winter and summer for the years 1978 to 1992 are discussed. In areas of significant correlations, the anticyclonicity time series for the duration 1965 to 1993 are examined. With two minor exceptions these time series show no identifiable trends during the 1978–1992 period.