Cai Chen, Stewart David J, Reid Jonathan P, Zhang Yun-hong, Ohm Peter, Dutcher Cari S, Clegg Simon L
The Institute of Chemical Physics, Key Laboratory of Cluster Science, Beijing Institute of Technology , Beijing 100081, People's Republic of China.
J Phys Chem A. 2015 Jan 29;119(4):704-18. doi: 10.1021/jp510525r. Epub 2015 Jan 15.
Measurements of the hygroscopic response of aerosol and the particle-to-gas partitioning of semivolatile organic compounds are crucial for providing more accurate descriptions of the compositional and size distributions of atmospheric aerosol. Concurrent measurements of particle size and composition (inferred from refractive index) are reported here using optical tweezers to isolate and probe individual aerosol droplets over extended timeframes. The measurements are shown to allow accurate retrievals of component vapor pressures and hygroscopic response through examining correlated variations in size and composition for binary droplets containing water and a single organic component. Measurements are reported for a homologous series of dicarboxylic acids, maleic acid, citric acid, glycerol, or 1,2,6-hexanetriol. An assessment of the inherent uncertainties in such measurements when measuring only particle size is provided to confirm the value of such a correlational approach. We also show that the method of molar refraction provides an accurate characterization of the compositional dependence of the refractive index of the solutions. In this method, the density of the pure liquid solute is the largest uncertainty and must be either known or inferred from subsaturated measurements with an error of <±2.5% to discriminate between different thermodynamic treatments.
测量气溶胶的吸湿响应以及半挥发性有机化合物的颗粒-气体分配对于更准确地描述大气气溶胶的成分和粒径分布至关重要。本文报道了使用光镊在较长时间内分离和探测单个气溶胶液滴，同时测量粒径和成分（由折射率推断）。通过检查含有水和单一有机成分的二元液滴的粒径和成分的相关变化，这些测量结果显示能够准确获取组分蒸气压和吸湿响应。报道了对一系列二元羧酸、马来酸、柠檬酸、甘油或1,2,6 -己三醇的测量。提供了仅测量粒径时此类测量中固有不确定性的评估，以证实这种相关方法的价值。我们还表明，摩尔折射法能够准确表征溶液折射率的成分依赖性。在这种方法中，纯液体溶质的密度是最大的不确定性因素，必须已知或通过过饱和测量推断，误差<±2.5%，以区分不同的热力学处理方法。
