With temperatures dropping to freezing on the sunshine coast just now, early evening 4 January 2019, we are also seeing a marked rise in PM2.5, increasing steeply above 50 ug/m³ today. The high atmospheric pressure is probably not helping matters, it's been above 1040 hpa (regularly above 1044 hPa) for most of the week.

A perfect storm of increased pollution due to rising domestic and business heating, and atmospheric conditions trapping pollutants and preventing their dispersal into a larger volume?