Estimation of\nthe Volatility and Apparent Activity\nCoefficient of Levoglucosan in Wood-Burning Organic Aerosols

Biomass burning (BB) is a major source of aerosols and\nblack carbon,\nthereby exerting an important impact on climate and air quality. Levoglucosan\nis the most well-recognized organic marker compound of BB and has\nbeen used to quantitatively assess BB’s contribution to ambient\naerosols. However, little is known about levoglucosan’s evaporation\nunder atmospheric conditions, primarily due to the uncertainty of\nits effective saturation vapor concentration (<i>C</i>*)\nand its unknown activity coefficient (γ), in the complex BB\nemission matrix. Here, we utilized a thermodenuder to investigate\nthe evaporation of levoglucosan from mixtures with polyethylene glycol\n(PEG) or BB primary organic aerosol (BBPOA) matrices, respectively.\nWe estimate a pure component log<sub>10</sub>(<i>C</i>*/[μg\nm<sup>–3</sup>]) of levoglucosan of 1.1 ± 0.1 at 298 K.\nWe reveal that levoglucosan mixed with PEG or BBPOA becomes more volatile\nthan when treated as a single component due to nonideal molecular\ninteractions. Considering that phase separation might occur in such\nsystems, we term γ apparent activity coefficient (γ<sub><i>a</i></sub>). We estimate log<sub>10</sub><i>C</i>* and γ<sub><i>a</i></sub> of levoglucosan in BBPOA\nof 1.8 ± 0.1 and 3.8 ± 0.3, assuming a liquid phase state.\nConsequently, γ<sub><i>a</i></sub> must be considered\nto avoid significant underestimation of levoglucosan evaporation via\ngas–particle partitioning during transport.