Gaseous and aerosol emissions from open burning of tree pruning and hedge trimming residues: Detailed composition and toxicity

Abstract

Gaseous and PM₁₀ samples were collected during the open burning of pruning residues (olive branches and garden waste) and characterised by distinct analytical techniques to obtain comprehensive chemical emission profiles. Oxidative potential (dithiothreoitol and ascorbic acid assays) and cell viability tests were also performed with the aim of evaluating aerosol toxicity. Emission factors (EFs) were as follows (g kg⁻¹ biofuel, dry basis): 1537–1672 for CO₂, 41.9–80 for CO, 2.74–6.6 for CH₄, 0.89–3.51 for ethane, 0.79–1.78 for ethylene and 0.56–3.47 for formaldehyde. Emissions of PM₁₀, organic carbon (OC) and elemental carbon (EC) were in the ranges 8–41, 3–18, and 0.4–1.5 g kg⁻¹ biofuel, dry basis, respectively. OC accounted for 35–45% of the total PM₁₀ mass, while EC contributed between around 3% and 5%. WSOC/OC ratios varied from 0.4 to 0.6, revealing that a substantial portion of the carbon emitted was hydrosoluble. Water soluble ions constituted around 8–21% of the PM₁₀ mass, with potassium and chloride as the most abundant ions in all samples. Levoglucosan, widely used a reliable biomass burning tracer, was found in significant amounts in all samples (up to 1.2% of the PM₁₀ mass). Retene, generally pointed out as a biomass combustion biomarker, was the predominant PAH. WSOC and some PAHs showed significant positive correlations with the intrinsic OP measured with the DTT assay, while the OP^AA was significantly correlated with some trace metals, such as Fe or Ni. All samples significantly reduced the viability of alveolar epithelial cells.