The bushfire (wildfire) event of the 2019/2020 southeastern Australian summer has been described as unprecedented. It was unprecedented because of the extent of the area burned and the ferocity at which burning occurred. Between September 2019 and February 2020, 12 million hectares (120 000 square km) of land across the eastern coasts of Australia burned. The fires led to the direct loss of 34 lives, the destruction of 3 500 houses and significant wildlife and habitat losses.
Smoke from fires severely reduced air quality across the entire south-eastern region of Australia, from Queensland in the north to Tasmania in the south. Long-range transport of smoke was observed to reach New Zealand on several occasions. Figure 1 includes an image from the satellite Himawari-8 on 21 December 2019 showing the locations of fires burning around the coastal rim of eastern Australia, and the smoke covering the entire region shown in the map. Also shown in Figure 1 are the PM2.5 particulate matter (particles with a diameter of ≤2.5 μm) concentrations over the region, predicted using the Australian Smoke Forecasting System (AQFx) that compares well to the smoke distribution shown on the Himawari-8 image. Information from AQFx was incorporated into air quality warnings issued by some State regulatory authorities during the bushfire event.
AQFx and the 2019/2020 summer fires
Figure 1. Himawari-8 visible image (red-green-blue composite imagery) of 21 December 2019. The AQFx forecast is an overlay of the national 27-km domain, the eastern 9-km domain, the Vic-Tas 3-km domain and the New South Wales 3-km domain.
Data from one air-quality monitoring station (AQMS), operated by regulatory authorities in each of the states of Queensland, New South Wales, Australian Capital Territory and Victoria are also presented here to illustrate the extent of the impact on air quality on south-eastern Australia.
The time series of PM2.5 particulate matter measured at each AQMS shown in Figure 2 illustrates the progression of the impact of smoke on air quality from the north to the south of south-eastern Australia, from early in the fire season in November 2019, when PM2.5 concentrations peaked in Queensland, to peaks in New South Wales in December 2019, to extremely high concentrations in the Australian Capital Territory in early January 2020 and peaks in Victoria in early to mid-January 2020. By the end of January 2020, PM2.5 concentrations had returned to more typical values.
Figure 2. Time series of daily averaged PM2.5 concentrations measured at AQMSs in Queensland, New South Wales, the Australian Capital Territory and Victoria.
The following services are acknowledged for their diligent efforts in collecting these data sets: Queensland Department of Environment Land and Water, New South Wales Department of Planning Industry and Environment, Australian Capital Territory Health Protection Service and Australian Capital Territory Environment Protection Authority.
The maximum daily PM2.5 concentrations during the smoke plumes measured by the AQMSs in all states were very high, in Queensland and New South Wales four times greater than the national standard (that is, a national environment protection measure for PM2.5 of 25 µg m-3 24-hour average), in Victoria eight times greater than the national standard, and in the Australian Capital Territory almost forty times greater. At the AQMS in the Australian Capital Territory the daily average PM2.5 concentration exceeded the national standard for 53 days between 1 November 2019 and 28 February 2020.
Smoke also had an impact on the Cape Grim Baseline Air Pollution Monitoring Station located in north-west Tasmania. Cape Grim is one of the Global Atmosphere Watch (GAW) Global Stations and has been operating for forty-four years. The hourly averaged black carbon (BC) time series for the period December 2019–February 2020 (Figure 3) shows smoke reaching Cape Grim on four occasions, with the highest BC concentrations observed on 3 January, peaking at over 4 µg m-3 (hourly averaged). The longest duration of smoke reaching the station occurred between 6–10 January (although with low BC concentrations) and 13–16 January (with higher BC concentrations). High BC concentrations were also observed on 31 January. Also shown in Figure 3 are air history maps for one hour in each of these periods, which show the circulation of air over south-east Australia before reaching Tasmania. The time series of BC is coloured by mean hourly ozone (O3) concentrations and shows an increase in ozone concentration measured at Cape Grim over the course of January. On 15, 16 and 31 January the ozone mole fraction levels reached 60 ppb or more. While these levels have been seen before during the four decades of ozone monitoring at Cape Grim, they have been exceptional events generally years apart. In the present case, they are associated with ageing of the smoke reaching Cape Grim.
|Figure 3. Time series of BC plotted as a function of ozone concentration (presented by the colour scale) at the Cape Grim Baseline Monitoring Station during January 2020. Air history maps from the UK Met Office. Source: Numerical Atmospheric-dispersion Modelling (NAME), UK Met Office, courtesy of A. Manning.
More than 10 million people are likely to have experienced some exposure to these very hazardous concentrations of PM2.5. Arriagada et al. (2020) have recently estimated that this exposure may be responsible for approximately 400 excess deaths, 1 120 hospital admissions for cardiovascular problems, 2 030 admissions for respiratory problems, and 1 300 emergency department attendances for asthma.