Investigation of the morphology and composition of aerosols from plant burning

Wildfires have significantly increased in frequency and intensity worldwide, driven by climate change, with urban expansion amplifying their impact on populations and structures near the wildland-urban interface. Combustion of biomass during vegetation fires produces complex aerosols that pose potential health risks through inhalation, ingestion, and dermal exposure. However, the understanding of aerosol morphology, composition, and behaviour remains incomplete. This study investigates the aerosols emitted during the combustion of Cistus monspeliensis, a Mediterranean shrub, under controlled laboratory conditions simulating wildfire scenarios. A full-scale combustion of a 1-m-high shrub was performed, enabling the capture of realistic emissions using an Electrical Low-Pressure Impactor +.

Aerosols were collected across different aerodynamic size fractions and analysed using scanning electron microscopy and energy dispersive X-ray spectroscopy. Particles were classified into four main types: soot aggregates, coarse fly ash (CFA), partially burnt particles, and condensed particles, with their morphology and elemental composition extensively characterized. Notably, potassium chloride condensates dominated smaller aerodynamic stages, while CFA exhibited high calcium and magnesium content in larger stages. Aerosol size and volume distributions revealed dynamic variations during combustion, with nanoparticles (43 nm aerodynamic diameter) prevailing before the heat release rate (HRR) peak and larger particles (69 nm aerodynamic diameter) dominating after the peak HRR.

The study also links particle physical characteristics to their aerodynamic behaviour, emphasizing the role of shape and density in discrepancies between measured and aerodynamic diameters. Deposition modelling using the Multiple-Path Particle Dosimetry model highlights potential health risks, particularly in the alveolar and tracheobronchial regions.

By integrating morphology, elemental composition, and size distribution, this research provides crucial insights into the characteristics of wildfire aerosols at their source, enhancing the understanding of their potential health implications. These findings contribute to the broader effort to model wildfire emissions and inform public health strategies, emphasizing the importance of studying aerosols under realistic combustion conditions.