Hygroscopic properties of levoglucosan and related organic compounds characteristic to biomass burning aerosol particles

[1] Biomass burning, which is characterized by pyrolysis as well as vaporization and condensation of biomass constituents, is a significant source of atmospheric organic aerosols. In this study, hygroscopic properties of five organic compounds (levoglucosan, D-glucose, and vanillic, syringic, and 4-hydroxybenozoic acids), which are major pyrolysis products of wood, were measured using a tandem differential mobility analyzer. Levoglucosan, which is typically the most abundant species in wood burning aerosols, showed a significant hygroscopic growth for particles with a diameter of 100 nm. No efflorescence was observed under the measured relative humidity, and a supersaturated condition of levoglucosan-water particles was observed. The growth factors of levoglucosan are 1.08, 1.18, 1.23, and 1.38 at relative humidity (RH) of 60, 80, 85, and 90%, respectively. The measured hygroscopic curves are in general consistent with those estimated from ideal solution theory and Uniquac Functional-Group Activity Coefficient (UNIFAC) and Conductor-Like Screening Model for Real Solvent (COSMO-RS) methods. Significant hygroscopic growth was also observed for D-glucose, whose growth factor is quite similar to that of levoglucosan. However, three model pyrolysis products of lignin (i.e., vanillic-, syringic-, and 4-hydroxybenzoic acids) did not show any hygroscopic growth under the RH conditions up to 95%. On the basis of the organic composition of wood burning aerosols, the water absorption attributed to levoglucosan in wood burning aerosols is calculated to be up to 30% of the organic mass at 90% RH. This study demonstrates that oxygenated organics emitted from biomass burning could significantly enhance the hygroscopic properties of atmospheric aerosols.

[1]生物质燃烧的特征是生物质成分的热解以及汽化和凝结，它是大气有机气溶胶的一个重要来源。在这项研究中，使用串联差分迁移率分析仪测量了五种有机化合物（左旋葡聚糖、D - 葡萄糖以及香草酸、丁香酸和4 - 羟基苯甲酸）的吸湿特性，这些化合物是木材的主要热解产物。左旋葡聚糖通常是木材燃烧产生的气溶胶中含量最丰富的物质，对于直径为100nm的颗粒显示出显著的吸湿增长。在测量的相对湿度下未观察到风化现象，并且观察到左旋葡聚糖 - 水颗粒的过饱和状态。在相对湿度（RH）为60%、80%、85%和90%时，左旋葡聚糖的增长因子分别为1.08、1.18、1.23和1.38。所测量的吸湿曲线总体上与根据理想溶液理论以及UNIFAC（通用似化学官能团活度系数）和COSMO - RS（真实溶剂的导体类屏蔽模型）方法估算的曲线一致。D - 葡萄糖也观察到显著的吸湿增长，其增长因子与左旋葡聚糖非常相似。然而，木质素的三种模型热解产物（即香草酸、丁香酸和4 - 羟基苯甲酸）在相对湿度高达95%的条件下未显示出任何吸湿增长。根据木材燃烧产生的气溶胶的有机成分，在90%相对湿度下，木材燃烧产生的气溶胶中归因于左旋葡聚糖的吸水量经计算可达有机质量的30%。这项研究表明，生物质燃烧排放的含氧有机物可显著增强大气气溶胶的吸湿特性。