Morphological and elemental characterization of fine and ultrafine particulate matter generated from fires

Fire emissions aggravate air pollution by releasing several hazardous pollutants, including respirable particulate matter (PM). Evidence on fires contribution to fine and ultrafine PM is scarce, principally in real fire scenarios. This study presents the first morphological and elemental composition of fine (PM_2.5, PM_156nm) and ultrafine (PM_50.4nm, PM_30.8nm, PM_14.9nm) fractions of PM released during three controlled structure (CSF) and two prescribed forest (PFF) fires. Total median PM levels were 9 times higher in CSF emissions than in PFF [11.13 (1.245-228.5) mg/m³versus 1.232 (0.5458-1.920) mg/m³), with fine PM being 13 and 3 times higher than ultrafine PM in CSF and PFF, respectively (p > 0.05). The morphological analysis revealed the prevalence of organic matter in fine/ultrafine PM, with several particles of bright contrast with distinct shapes and sizes, which were more prominent in PFF. The electron dispersive spectroscopy and elemental mapping analysis suggested the presence of sulphates, carbonates, and chlorides of sodium, magnesium, potassium, and calcium (biomass combustion), and stainless-steel particles associated with handling of heavy machinery in PFF. Also, particles of PbCl₂ and PbO (combustion of paints/solder) were observed in CSF. Zn, Cu, Cr, and Ni, as well as Co (in PFF), and Pb (in CSF) were the predominant elements in fire generated PM. Toxic and (possible/probable) carcinogenic elements represented up to 29.3 % and 33.1 % of fine and ultrafine fire generated PM, respectively. This work advances the knowledge on fire-generated PM highlighting the need for further studies on fire chemistry, PM behaviour, and realistic huma exposure and health risk assessments.