A comprehensive assessment of emissions from prescribed fires in two Mediterranean shrublands: chemical and morphological analysis

Abstract. Prescribed fires were conducted in two shrubland communities dominated by Genista hispanica subsp. occidentalis and Calluna vulgaris in La Cueta, León, Spain, to characterise particulate and gaseous emissions during combustion. Distinct fire dynamics were observed: Calluna exhibited a Modified Combustion Efficiency (MCE) of 90.6, indicative of flaming combustion, while Genista showed an MCE of 70.8, characteristic of smouldering conditions. Gas-phase analysis revealed notably higher concentrations of CO₂, CO, CH₄, C₂H₆, and total organic carbon (TOC) in Calluna compared to Genista, with CO₂ showing the greatest difference. Conversely, Genista exhibited slightly elevated NO and NO₂ levels. Most gas concentrations were higher for Calluna, except for hydrogen fluoride (HF), which was more abundant in Genista. Elemental carbon (EC) and organic carbon (OC) accounted for 28.1 % and 32.9 % of PM_2.5 mass in Calluna and Genista, respectively. Water-soluble inorganic ions contributed 6.9 % and 4.5 % to PM_2.5 mass, with most ions more abundant in Calluna, except chloride (Cl⁻), which was higher in Genista. In both cases, Cl^-, SO₄^2-, Na⁺, Mg²⁺, and Ca²⁺ dominated the ionic composition. Morphological analysis revealed a population dominated by tar balls (submicrometer spherical particles) and aggregates with thick organic coatings. Derived emission factors are expected to provide valuable input for numerical models evaluating the impacts of prescribed and unplanned forest fires in the Mediterranean region.