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Abstract

Fires in vegetation commonly occur in environments where they have an impact not only on vegetation but also on soil and atmosphere. Arson is a common reason for such fires and might influence areas of various size. One of such fires occurred in Sosnowiec (Poland) in May 2024 and covered an area of a few tens of square meters. 35 samples of plants altered to various degrees and soils were collected and investigated using reflected light microscopy, SEM, gas chromatography-mass spectrometry (GC-MS), and flash pyrolysis/GC-MS. On the basis of reflectance measurements, the burning temperature was estimated at 200-435 °C. In individual spots, the temperature differed resulting in various alterations of vegetation. Some plants were completely charred, others were charred only from outside while internal parts were not affected by the temperature. Very thin cell walls of some vegetation suggest that the most external parts of plants might have been completely burnt or formed a few µm in size charred particles incorporated into soil or emitted into the atmosphere. Limited impact of fires on soil is reflected in the occurrence of unaltered vegetation together vegetation altered to various degrees. The obtained results showed that the estimated fires led to generation of a substantial amounts of organic compounds comprising products of incomplete combustion such as polycyclic aromatic hydrocarbons (PAHs) and phenolic lignin degradation products. PAHs distribution was dominated by 3- and 4-rings compounds whereas heavier 5-ring PAHs occurred in minority. Phenolic compounds produced during pyrolysis of lignin are fractionated into three fractions: volatile phenols that are removed with gases (phenols and cresols), compounds included in pyrolysates and macromolecular remains. Due to demethoxylation lignin-derived phenols significantly changed their distribution being the fingerprint of their biological origin. The shift was more noticeable with increasing fire temperature.