Transport of Pollutants from Pilliga Forest Wildfires in Northern New South Wales in December 2023 and Its Impact on Air Quality in New South Wales

In mid-December 2023, a large wildfire occurred in Pilliga Forest at Duck Creek, about 20 km south of the town of Narrabri in northern New South Wales. The fire was caused by lightning. It quickly spread due to high temperature at the start of the austral summer. At the end of the fire, about 130,000 ha of forest and bushland were burned. Even though it was not large compared to the Black Summer megafires 4 years before in 2019 which was also started in northern New South Wales near the coast, this Pilliga Forest wildfire had a widespread impact on air quality over a number of towns and cities in the central and coastal New South Wales areas including the Hunter regions and metropolitan area of Sydney. Ground air quality monitoring stations, remote sensing data from satellites, upper air measurements from ceilometer lidars and air quality model WRF-Chem (V4.4.2) are used in this study to analyse the dispersion and transport of air pollutants from the fire emission at Pilliga Forest. The model results give insights on the vertical structure of transported plumes which is also compared and validated with aerosol profiles from ceilometer data at Merriwa and Lidcombe, the Aerosol Optical Depth (AOD) from the sun photometer and the global CAMS forecast data and MERRA reanalysis data. Wildfires in remote forest areas by their nature are spontaneous but they can have widespread effect on air quality in populated areas far from the fire sources. The WRF-Chem air quality model predicted the dispersion and transport of pollutants emitted from the Pilliga fires corresponded well with the remote sensing and meteorological surface data. However, it did not predict correctly the 1-hourly peak pollutants occurring simultaneously in the Sydney region on the 19/12/2023 at 15:00 AEST (Australia Eastern Standard Time). Lessons on the future preparation of these types of wildfires with respect to air quality modelling and air pollution forecasting in the metropolitan areas will be discussed.