Among the organic compounds emitted during biomass burning events, methoxyphenols (45%wt. of the particulate matter derived from wood smoke) are present both in the gas and particle phases, and may undergo various transformations during atmospheric ageing induced either by light (photochemistry) or temperature (thermal processes). We report here chemical and optical analyses of syringol (C8H10O3) particles, one of the most abundant methoxyphenol species found in such biomass burning plumes, after both photo- and thermal-ageing. Chemical analyses were performed using a HESI/LC/DAD/MS (orbitrap mass spectrometry). When exposed to UV-light or heated for several hours, syringol became yellowish in both cases while distinct products were identified. The differences in chemistry propagate also to the optical properties of the aerosols as probed by broad band cavity enhanced spectroscopy (BBCES). These results, when considered together, may be of importance considering the possible effects on human health of these detected ageing-products and the contribution to the radiative forcing. This work is supported by the Ministère des Affaires Etrangères et du Développement International (France) and the Ministry of Science (Israel), under the Research Program "Maïmonide-Israel". Two groups collaborate for it: Christian George group (CNRS, FRANCE) for the high resolution MS chemical analyses and Yinon Rudich group (Weizmann Institute, ISRAEL) for the optical properties of aerosols.