Al-Mashala Habeeb H, Schervish Meredith, Liyanage Sithumi M, Barton Jace A, Shiraiwa Manabu, Schnitzler Elijah G
Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078, United States.
Department of Chemistry, University of California Irvine, Irvine, California 92697, United States.
ACS EST Air. 2025 Mar 31;2(4):637-647. doi: 10.1021/acsestair.4c00345. eCollection 2025 Apr 11.
Biomass burning is one of the most significant sources of organic aerosol in the atmosphere. Biomass burning organic aerosol (BBOA) has been observed to undergo liquid-liquid phase separation (LLPS) to give core-shell morphology with the hydrophobic phase encapsulating the hydrophilic phase, potentially impacting the evolution of light-absorbing components, i.e., brown carbon (BrC), through multiphase processes. Here, we demonstrate how multiphase processing differs between the water-soluble (i.e., hydrophilic) and insoluble (i.e., hydrophobic) phases of BBOA in terms of reactive uptake of ozone in a coated-wall flow tube. Effects of relative humidity (RH) and ultraviolet (UV) irradiation were investigated. Experimental timeseries were used to inform simulations using multilayer kinetic modeling. Among non-irradiated thin films, the uptake coefficient was greatest for the water-soluble phase at 75% RH (3 × 10, corresponding to a diffusion coefficient of BrC, , of 3 × 10 cm s) and least for the same phase at 0% RH (1 × 10, corresponding to of 1 × 10 cm s). The uptake coefficient for the water-insoluble phase fell between these two (about 1.5 × 10), regardless of RH, and the corresponding increased only slightly (8 × 10 cm s at 0% RH to 9 × 10 cm s at 75% RH). The uptake coefficients of both phases at 0% RH decreased significantly after UV irradiation, consistent with a transition from viscous liquid to solid and supported by qualitative microscopy observations. Modeling multiphase ozone oxidation of primary BrC components in the atmosphere demonstrated, first, that LLPS may extend the lifetime of water-soluble BBOA encapsulated by water-insoluble species by a factor of 1.5 at moderate to high RH and, also, that UV irradiation may extend the lifetime of both phases by more than a factor of 2.5.
生物质燃烧是大气中有机气溶胶的最重要来源之一。已观察到生物质燃烧有机气溶胶（BBOA）会发生液-液相分离（LLPS），形成核壳形态，疏水相包裹亲水相，这可能通过多相过程影响吸光成分即棕碳（BrC）的演变。在此，我们展示了在涂壁流动管中，BBOA的水溶性（即亲水）相和不溶性（即疏水）相在臭氧反应吸收方面的多相过程有何不同。研究了相对湿度（RH）和紫外线（UV）照射的影响。利用多层动力学模型，通过实验时间序列为模拟提供信息。在未照射的薄膜中，水溶性相在75%相对湿度下的吸收系数最大（3×10，对应BrC的扩散系数，为3×10 cm² s⁻¹），在0%相对湿度下最小（1×10，对应为1×10 cm² s⁻¹）。无论相对湿度如何，水不溶性相的吸收系数介于两者之间（约1.5×10），且相应的仅略有增加（从0%相对湿度下的8×10 cm² s⁻¹增加到75%相对湿度下的9×10 cm² s⁻¹）。在0%相对湿度下，紫外线照射后两相的吸收系数均显著降低，这与从粘性液体向固体的转变一致，定性显微镜观察也支持这一点。对大气中初级BrC成分的多相臭氧氧化建模表明，首先，在中高相对湿度下，液-液相分离可能使被水不溶性物质包裹的水溶性BBOA的寿命延长1.5倍，其次，紫外线照射可能使两相的寿命延长超过2.5倍。
