Trace elements and nutrients in wildfire plumes to the southeast of Australia

The unprecedented magnitude of the 2019-20 Australian fires have raised interest in the potential for fire emissions to supply vital nutrients to remote ocean regions. Fire emissions are episodic and unpredictable, making them difficult to investigate. Here we present results from continuous monitoring of the atmospheric composition at the kunanyi/Mount Wellington time-series station, in southeastern Tasmania (Australia) between 2016 and 2020. Characterization of aerosols at the station revealed a striking increase in the atmospheric loading of iron (Fe), nitrate (NO3-), ammonium (NH4+) and manganese (Mn) associated with fire events. High concentrations of mineral dust in fire-impacted aerosols evidenced that strong pyro-convective winds resulted in the erosion and entrainment of soil particles into the atmosphere alongside the fire plume. Enrichment factor (EF) analysis in aerosols suggested that soil dominated the atmospheric loading of Fe and Mn in fire emissions. Lead (Pb) enrichment in fire aerosols (EFPb > 10) was attributed to the resuspension of soil historically contaminated by leaded petrol and mining operations. Finally, atmospheric transport was showed to play a key role in decreasing concentrations of total Fe (T-Fe) and mineral dust while increasing the aeolian content of bioaccessible Fe (L-Fe), NO3- and NH4+ in the plume downwind of the fires. As future projections suggest an increase in fire activity worldwide, atmospheric time-series stations such as kunanyi/Mount Wellington are key to better understand future impacts of fire emissions on human health and natural ecosystems.