Measurements of the evaporation and hygroscopic response of single fine-mode aerosol particles using a Bessel beam optical trap
Measurements of the evaporation and hygroscopic response of single fine-mode aerosol particles using a Bessel beam optical trap
复制标题
DOI：
10.1039/c3cp54368d
复制
发表时间：
2014-01-01
影响因子：
3.3
通讯作者：
Reid, Jonathan P.
中科院分区：
文献类型：
--
作者：
Cotterell, Michael I.;Mason, Bernard J.;Reid, Jonathan P.
一束水平传输的零级贝塞尔激光和反向传播的气流被用来限制单个精细模气溶胶粒子在较长的时间内，在此期间进行了过程测量。通过分析贝塞尔光束中粒子在532 nm处的散射角变化来测量粒子的尺寸，使用405 nm或633 nm的探针束。甘油和1，2，6-己三醇颗粒的蒸汽压分别为7.5+/-2.6 Mpa和0.20+/-0.02 Mpa。己三醇的低挥发性使其能够更好地定义测量时间段内的诱捕环境相对湿度分布，因此与甘油相比，获得了更高的测量精度。用405 nm探针束采集相函数，模拟了正己三醇粒子沿贝塞尔光束传播长度的位置，确定了粒子的尺寸演化及其在532 nm和405 nm波长处的折射率。在半径为350 nm的颗粒上测量了氯化钠和硫铵的吸湿生长，生长曲线可以用广泛使用的平衡态模型很好地描述。这些是测量了单颗粒吸湿性的最小颗粒，代表了对精细模式和近累积模式气溶胶吸湿性的首次测量，在负载、光消光和散射方面，大小区域具有最大的大气相关性。最后，将该方法与其他单粒子方法和集成方法进行了对比，并对其局限性进行了评估。
A single horizontally-propagating zeroth order Bessel laser beam with a counter-propagating gas flow was used to confine single fine-mode aerosol particles over extended periods of time, during which process measurements were performed. Particle sizes were measured by the analysis of the angular variation of light scattered at 532 nm by a particle in the Bessel beam, using either a probe beam at 405 nm or 633 nm. The vapour pressures of glycerol and 1,2,6-hexanetriol particles were determined to be 7.5 +/- 2.6 mPa and 0.20 +/- 0.02 mPa respectively. The lower volatility of hexanetriol allowed better definition of the trapping environment relative humidity profile over the measurement time period, thus higher precision measurements were obtained compared to those for glycerol. The size evolution of a hexanetriol particle, as well as its refractive index at wavelengths 532 nm and 405 nm, were determined by modelling its position along the Bessel beam propagation length while collecting phase functions with the 405 nm probe beam. Measurements of the hygroscopic growth of sodium chloride and ammonium sulfate have been performed on particles as small as 350 nm in radius, with growth curves well described by widely used equilibrium state models. These are the smallest particles for which single-particle hygroscopicity has been measured and represent the first measurements of hygroscopicity on fine mode and near-accumulation mode aerosols, the size regimes bearing the most atmospheric relevance in terms of loading, light extinction and scattering. Finally, the technique is contrasted with other single particle and ensemble methods, and limitations are assessed.