Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada.
Department of Chemistry, University of California, Irvine, Irvine, California 92697, United States.
Environ Sci Technol. 2023 Oct 3;57(39):14548-14557. doi: 10.1021/acs.est.3c03231. Epub 2023 Sep 20.
Smoke particles generated by burning biomass consist mainly of organic aerosol termed biomass burning organic aerosol (BBOA). BBOA influences the climate by scattering and absorbing solar radiation or acting as nuclei for cloud formation. The viscosity and the phase behavior (i.e., the number and type of phases present in a particle) are properties of BBOA that are expected to impact several climate-relevant processes but remain highly uncertain. We studied the phase behavior of BBOA using fluorescence microscopy and showed that BBOA particles comprise two organic phases (a hydrophobic and a hydrophilic phase) across a wide range of atmospheric relative humidity (RH). We determined the viscosity of the two phases at room temperature using a photobleaching method and showed that the two phases possess different RH-dependent viscosities. The viscosity of the hydrophobic phase is largely independent of the RH from 0 to 95%. We use the Vogel-Fulcher-Tamman equation to extrapolate our results to colder and warmer temperatures, and based on the extrapolation, the hydrophobic phase is predicted to be glassy (viscosity >10 Pa s) for temperatures less than 230 K and RHs below 95%, with possible implications for heterogeneous reaction kinetics and cloud formation in the atmosphere. Using a kinetic multilayer model (KM-GAP), we investigated the effect of two phases on the atmospheric lifetime of brown carbon within BBOA, which is a climate-warming agent. We showed that the presence of two phases can increase the lifetime of brown carbon in the planetary boundary layer and polar regions compared to previous modeling studies. Hence, the presence of two phases can lead to an increase in the predicted warming effect of BBOA on the climate.
燃烧生物质产生的烟雾颗粒主要由有机气溶胶组成，称为生物质燃烧有机气溶胶（BBOA）。BBOA 通过散射和吸收太阳辐射，或作为云形成的核心，影响气候。粘度和相行为（即颗粒中存在的相的数量和类型）是预计会影响几个与气候相关的过程但仍然高度不确定的 BBOA 特性。我们使用荧光显微镜研究了 BBOA 的相行为，并表明 BBOA 颗粒在很宽的大气相对湿度（RH）范围内包含两种有机相（疏水性和亲水性相）。我们使用光漂白法在室温下确定了两种相的粘度，并表明两种相具有不同的 RH 依赖性粘度。疏水性相的粘度在 0 到 95%的 RH 范围内基本不受 RH 的影响。我们使用 Vogel-Fulcher-Tamman 方程将我们的结果外推到更冷和更温暖的温度，并基于外推，预测疏水性相在温度低于 230 K 和 RH 低于 95%时为玻璃态（粘度>10 Pa s），这可能对非均相反应动力学和大气中的云形成有影响。使用动力学多层模型（KM-GAP），我们研究了两种相对 BBOA 中棕色碳大气寿命的影响，棕色碳是一种气候变暖剂。我们表明，与以前的建模研究相比，两种相的存在可以增加棕色碳在行星边界层和极地地区的大气寿命。因此，两种相的存在可能会导致 BBOA 对气候的变暖效应预测增加。
