Ground‐Based Field Measurements of PM2.5 Emission Factors From Flaming and Smoldering Combustion in Eucalypt Forests

In fire‐prone areas such as southern Australia and parts of the United States, prescribed burning is a common fire management tool to reduce fuel load for wildfire suppression purposes. The burns are typically undertaken during calm and stable conditions when the burn extent and duration can be carefully controlled. This often coincides with poor atmospheric ventilation, leading to a buildup of smoke, which can impact air quality and human health. The low intensity of these burns also means that the plume is less buoyant and the main impact on local populations is due to emissions during the slow and prolonged smoldering combustion of heavy fuels. This study presents emission measurements of PM 2.5 at prescribed burns in eucalypt forests of southern Australia using a smoke collection method suitable for both flaming combustion of fine fuels and residual smoldering combustion of heavy fuels and logs. The median PM 2.5 emission factors (EFs) measured were 16.9‐g/kg fuel during flaming combustion and 38.8‐g/kg fuel during smoldering combustion. The correlation between PM 2.5 EFs and modified combustion efficiency highlights two distinct trends at low modified combustion efficiency, attributed to the distinct combustion processes of glowing char combustion and pyrolysis. Hence, two distinct relationships were developed that best fitted the measurements and that can be used to extrapolate measured EFs to a wider range of fuel and burning conditions. The results from this study addressed a gap in our knowledge of particle emissions during burns in eucalypt forests under different burning conditions and help to better forecast and manage air quality impacts from prescribed burns on nearby communities.