Aerosols and carbonaceous and nitrogenous compounds emitted during the combustion of dead shrubs according to twigs’ diameter and combustion phases

Abstract

Smoke from forest fires is hazardous to health and can result in losses of respiratory function and vision. The knowledge of the chemical constituents in such smoke is an important objective. In this study, leaves and branches and twigs of Cistus Monspeliensis were burned with a cone calorimeter and the emitted smoke was analysed by non-dispersive infrared (NDIR) spectroscopy, He–Ne laser method, Fourier-transform infrared (FTIR) spectroscopy, and automated thermal-desorption–gas-chromatography/mass-spectrometry (ATD-GC/MS). These techniques were used during various combustion phases: prior to ignition and during flaming and glowing phases. The influence of branch diameter on chemical composition was examined. Analysis of the smoke reveals the presence of CO2, H2O, CO, aerosols, CH4, NO, and other gases in smaller proportions, as well as non-methane organic compounds (NMOCs). 96% of the carbon present in the fuel was found in the emitted smoke. CO2 is the gas mainly emitted and its level is independent of the diameter of the cistus branch burned. It is mainly emitted in the flaming phase, unlike CO, which is emitted during the glowing phase. Aerosols are emitted principally during the pre-ignition stage. The mass loss is higher during the flaming phase than during the glowing one because the burning occurs under well-ventilated condition. During the glowing phase, the mass loss is only due to the char oxidation. The calculation of the modified combustion efficiency confirms those operating conditions.