Ambient black carbon particle hygroscopic properties controlled by mixing state and composition
Ambient black carbon particle hygroscopic properties controlled by mixing state and composition
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DOI：
10.5194/acp-13-2015-2013
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发表时间：
2013-01-01
影响因子：
6.3
通讯作者：
Bandy, B.
中科院分区：
文献类型：
--
作者：
Liu, D.;Allan, J.;Bandy, B.
大气中黑碳气溶胶（BC）的湿法去除是决定其大气寿命、垂直和水平分布、局部和区域尺度的扩散以及直接、半直接和间接辐射强迫效应的关键因素。通过混凝或涂层工艺获得更亲水的成分后，新排放的疏水性BC的云内清除和湿沉积率将增加。对于大多数模型输入而言，BC 的寿命仍然存在相当大的不确定性，这很大程度上是由于现场观测数据对 BC 疏水到亲水转化过程的约束不足。这项研究是在英国诺福克北部海岸线的一个地点进行的，BC 颗粒是从西欧不同地区运来的。吸湿性串联微分迁移率分析仪 (HTDMA) 与单颗粒烟灰光度计 (SP2) 相结合，实时测量 BC 颗粒的吸湿特性和相关的混合状态。此外，烟灰颗粒 AMS (SP-AMS) 还测量了与 BC 颗粒相关的其他材料的化学成分。 BC 颗粒整体始终包含吸湿性较低的模式，生长因子 (gf) 在 90% RH（干燥直径 163 nm）下约为 1.05。重要的是，在整个实验过程中观察到了BC颗粒的吸湿性更强的模式，这些BC颗粒的gf扩展到类似于1.4-1.6，该模式与吸湿性较小的模式之间的最小值约为1.25，或者等效的有效吸湿性参数kappa类似于0.1。 BC颗粒的gf (gf(BC))很大程度上受相关可溶性物质组成的影响：gfBC的增加与次要无机组分有关，并且当BC颗粒中含有硝酸铵时，这些增加更加明显；然而，次生有机物的存在将 gf(BC) 抑制到低于纯无机物的水平。与测量结果相比，Zdanovskii-Stokes-Robinson (ZSR) 混合规则捕获了不同成分的吸湿性贡献，误差在 +/- 30% 范围内，但由于 BC 组分的复杂形态以及与 HTDMA 测量的半挥发性颗粒相关的潜在人为因素，该规则存在不确定性。这项研究提供了关于BC吸湿性与其混合状态相关的详细见解，其结果将重要地约束各种高级模型所使用的BC的微观物理混合方案。特别是，这提供了直接证据，强调需要考虑BC颗粒的硝酸铵老化，因为这将导致颗粒在比硫酸盐形成短得多的时间尺度内变得亲水，而硫酸盐形成通常是唯一考虑的机制。
The wet removal of black carbon aerosol (BC) in the atmosphere is a crucial factor in determining its atmospheric lifetime and thereby the vertical and horizontal distributions, dispersion on local and regional scales, and the direct, semi-direct and indirect radiative forcing effects. The in-cloud scavenging and wet deposition rate of freshly emitted hydrophobic BC will be increased on acquisition of more-hydrophilic components by coagulation or coating processes. The lifetime of BC is still subject to considerable uncertainty for most of the model inputs, which is largely due to the insufficient constraints on the BC hydrophobic-to-hydrophilic conversion process from observational field data. This study was conducted at a site along UK North Norfolk coastline, where the BC particles were transported from different regions within Western Europe. A hygroscopicity tandem differential mobility analyser (HTDMA) was coupled with a single particle soot photometer (SP2) to measure the hygroscopic properties of BC particles and associated mixing state in real time. In addition, a Soot Particle AMS (SP-AMS) measured the chemical compositions of additional material associated with BC particles. The ensemble of BC particles persistently contained a less-hygroscopic mode at a growth factor (gf) of around 1.05 at 90% RH (dry diameter 163 nm). Importantly, a more-hygroscopic mode of BC particles was observed throughout the experiment, the gf of these BC particles extended up to similar to 1.4-1.6 with the minimum between this and the less hygroscopic mode at a gf similar to 1.25, or equivalent effective hygroscopicity parameter kappa similar to 0.1. The gf of BC particles (gf(BC)) was highly influenced by the composition of associated soluble material: increases of gfBC were associated with secondary inorganic components, and these increases were more pronounced when ammonium nitrate was in the BC particles; however the presence of secondary organic matter suppressed the gf(BC) below that of pure inorganics. The Zdanovskii-Stokes-Robinson (ZSR) mixing rule captures the hygroscopicity contributions from different compositions within +/- 30% compared to the measured results, however is subject to uncertainty due to the complex morphology of BC component and potential artefacts associated with semivolatile particles measured with the HTDMA. This study provides detailed insights on BC hygroscopicity associated with its mixing state, and the results will importantly constrain the microphysical mixing schemes of BC as used by a variety of high level models. In particular, this provides direct evidence to highlight the need to consider ammonium nitrate ageing of BC particles because this will result in particles becoming hydrophilic on much shorter timescales than for sulphate formation, which is often the only mechanism considered.