Accurate Measurements of Aerosol Hygroscopic Growth over a Wide Range in Relative Humidity.
Accurate Measurements of Aerosol Hygroscopic Growth over a Wide Range in Relative Humidity.
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DOI：
10.1021/acs.jpca.6b04194
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发表时间：
2016-06
期刊：
影响因子：
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通讯作者：
G. Rovelli;R. E. H. Miles;J. Reid;S. Clegg
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文献类型：
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作者：
G. Rovelli;R. E. H. Miles;J. Reid;S. Clegg
使用比较蒸发动力学方法，我们描述了一种用于确定气溶胶液滴平衡吸湿增长的新且准确的方法。当含水液滴蒸发到与气相相对湿度平衡的稳定尺寸和组成时，含水液滴的随时间变化的尺寸用于确定水的随时间变化的质量通量，从而产生关于液滴表面上方的水在每个时刻的蒸汽压的信息。通过对具有已知平衡特性的液滴（纯水滴或氯化钠液滴）的蒸发曲线进行控制测量，可以提供气相相对湿度的准确表征。结合起来，并通过与考虑控制液滴蒸发动力学的热量和质量传输的模拟进行比较，这些测量允许准确检索溶液液滴的平衡性质（即，溶质的质量分数、直径增长因子、渗透系数或每个溶质分子的水分子数随水活度的变化）。吸湿性测量可以在水活度的宽范围内进行（从>0.99到原则上0.9和80%RH以下的±1%，直径增长因子的最大不确定性为± 0.7%。对于所有的无机系统检查，时间依赖性的数据是一致的质量容纳（或蒸发）系数的大值（>0.1）。
Using a comparative evaporation kinetics approach, we describe a new and accurate method for determining the equilibrium hygroscopic growth of aerosol droplets. The time-evolving size of an aqueous droplet, as it evaporates to a steady size and composition that is in equilibrium with the gas phase relative humidity, is used to determine the time-dependent mass flux of water, yielding information on the vapor pressure of water above the droplet surface at every instant in time. Accurate characterization of the gas phase relative humidity is provided from a control measurement of the evaporation profile of a droplet of know equilibrium properties, either a pure water droplet or a sodium chloride droplet. In combination, and by comparison with simulations that account for both the heat and mass transport governing the droplet evaporation kinetics, these measurements allow accurate retrieval of the equilibrium properties of the solution droplet (i.e., the variations with water activity in the mass fraction of solute, diameter growth factor, osmotic coefficient or number of water molecules per solute molecule). Hygroscopicity measurements can be made over a wide range in water activity (from >0.99 to, in principle, 0.9 and ∼±1% below 80% RH, and maximum uncertainties in diameter growth factor of ±0.7%. For all of the inorganic systems examined, the time-dependent data are consistent with large values of the mass accommodation (or evaporation) coefficient (>0.1).