“…20 The concentration of organic aerosol (OA) particle mass has been documented to increase up to 7 times during photochemical aging (Grieshop et al, 2009;Heringa et al, 2011;Ortega et al, 2013;Bruns et al, 2015;Tiitta et al, 2016), however, the chemical composition of this secondary organic aerosol (SOA) produced remains uncertain. Multiple studies investigated the oxidation of specific gas-phase precursors commonly emitted by biomass burning, namely methoxyphenols (Net et al, 2011;Lauraguais et al, 2012;Yee et al, 2013;Lauraguais et al, 2014), but few have specifically addressed the 25 aging of specific biomass burning tracers in the particle phase (Hennigan et al, 2010;Kessler et al, 2010;Lai et al, 2014), and so far, only Fortenberry et al (2017) have attempted characterizing the aged chemical fingerprint of biomass burning emissions at the molecular level by means of a Thermal Desorption Aerosol Gas Chromatograph (TAG) connected to a Potential Aerosol Mass (PAM) flow reactor. This is especially important in the context of source apportionment studies which assume that chemical profiles are constant with time.…”