Investigation of particle and vapor wall-loss effects on controlled wood-smoke smog-chamber experiments
Investigation of particle and vapor wall-loss effects on controlled wood-smoke smog-chamber experiments
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DOI：
10.5194/acp-15-11027-2015
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发表时间：
2015-01-01
影响因子：
6.3
通讯作者：
Pierce, J. R.
中科院分区：
文献类型：
--
作者：
Bian, Q.;May, A. A.;Pierce, J. R.
烟雾室被广泛用于研究驱动大气中气体和颗粒演变的过程。这些实验的一个局限性是，颗粒和气相物种可能会失去室壁在较短的时间尺度比大气过程的时间尺度正在研究的室实验。这些颗粒和蒸汽壁损失已在最近的二次有机气溶胶（SOA）形成的研究中进行了研究，但它们还没有被系统地研究在燃烧的一次排放的实验。由于气体/颗粒和气体/壁之间的竞争，燃烧排放物（例如来自木材烟雾）的半挥发性性质可能使实验过程中室内颗粒和蒸汽壁沉积的行为复杂化。在这些实验中，蒸汽损失到壁可能会影响颗粒蒸发，并且燃烧形成SOA的潜在前体可能会损失到壁，导致低估气溶胶产量。在这里，我们进行模拟，以确定如何粒子和气相壁损失有助于观察到的演变的气溶胶在第三消防实验室在米苏拉实验（火焰III）的实验。我们使用的两个时刻气溶胶截面（TOMAS）微物理算法加上有机挥发性基组（VBS）和壁损失配方来检查颗粒和蒸汽壁损失的预测程度。我们将我们的研究范围限制在光氧化之前的黑暗时期，以简化气溶胶系统的初步研究。我们的模型模拟表明，超过三分之一的初始颗粒相有机质量（41%）在实验过程中损失，超过一半的这种颗粒有机质量损失是从直接颗粒壁损失（65%的损失），其余的从蒸汽损失驱动的颗粒蒸发到壁（35%的损失）。我们进行了一系列的敏感性测试，以了解我们的模拟中的不确定性。在初始木材烟雾挥发性分布的不确定性贡献了18%的不确定性，最终颗粒有机质量留在室内（相对于基本假设模拟）。我们表明，总质量损失可能取决于相对于壁的蒸汽的有效饱和浓度，因为这些值目前在文献中变化很大。烟雾室填充过程中烟雾稀释的细节可能会影响到墙壁的质量损失，在实验过程中，与我们假设颗粒和蒸汽最初在室内处于平衡状态的模拟相比，稀释度为25：1的颗粒有机物质量损失增加了33%。最后，我们讨论了我们的研究结果可能会影响木材烟雾室实验中的排放因子和SOA生产的解释。
Smog chambers are extensively used to study processes that drive gas and particle evolution in the atmosphere. A limitation of these experiments is that particles and gas-phase species may be lost to chamber walls on shorter timescales than the timescales of the atmospheric processes being studied in the chamber experiments. These particle and vapor wall losses have been investigated in recent studies of secondary organic aerosol (SOA) formation, but they have not been systematically investigated in experiments of primary emissions from combustion. The semi-volatile nature of combustion emissions (e.g. from wood smoke) may complicate the behavior of particle and vapor wall deposition in the chamber over the course of the experiments due to the competition between gas/particle and gas/wall partitioning. Losses of vapors to the walls may impact particle evaporation in these experiments, and potential precursors for SOA formation from combustion may be lost to the walls, causing underestimations of aerosol yields. Here, we conduct simulations to determine how particle and gas-phase wall losses contributed to the observed evolution of the aerosol during experiments in the third Fire Lab At Missoula Experiment (FLAME III). We use the TwO-Moment Aerosol Sectional (TOMAS) microphysics algorithm coupled with the organic volatility basis set (VBS) and wall-loss formulations to examine the predicted extent of particle and vapor wall losses. We limit the scope of our study to the dark periods in the chamber before photo-oxidation to simplify the aerosol system for this initial study. Our model simulations suggest that over one-third of the initial particle-phase organic mass (41 %) was lost during the experiments, and over half of this particle-organic mass loss was from direct particle wall loss (65% of the loss) with the remainder from evaporation of the particles driven by vapor losses to the walls (35% of the loss). We perform a series of sensitivity tests to understand uncertainties in our simulations. Uncertainty in the initial wood-smoke volatility distribution contributes 18% uncertainty to the final particle-organic mass remaining in the chamber (relative to base-assumption simulation). We show that the total mass loss may depend on the effective saturation concentration of vapor with respect to the walls as these values currently vary widely in the literature. The details of smoke dilution during the filling of smog chambers may influence the mass loss to the walls, and a dilution of similar to 25 : 1 during the experiments increased particle-organic mass loss by 33% compared to a simulation where we assume the particles and vapors are initially in equilibrium in the chamber. Finally, we discuss how our findings may influence interpretations of emission factors and SOA production in wood-smoke smog-chamber experiments.