A complete parameterisation of the relative humidity and wavelength dependence of the refractive index of hygroscopic inorganic aerosol particles
A complete parameterisation of the relative humidity and wavelength dependence of the refractive index of hygroscopic inorganic aerosol particles
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DOI：
10.5194/acp-17-9837-2017
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发表时间：
2017-08-22
影响因子：
6.3
通讯作者：
Reid, Jonathan P.
中科院分区：
文献类型：
--
作者：
Cotterell, Michael I.;Willoughby, Rose E.;Reid, Jonathan P.
气溶胶辐射强迫的计算需要与波长有关的气溶胶光学性质的知识，例如单次散射反照率。这些气溶胶光学性质可以利用Mie理论从颗粒大小和折射率等关键微观物理性质的知识中计算出来，假设大气颗粒被很好地近似为球形和均匀的。我们给出了含有与大气相关的关键无机溶质：氯化钠、硝酸铵、(NH4)(2)SO4、NH4HSO4和Na2SO4的水相气溶胶粒子的折射率测定，报告了折射率随波长(400-650 nm)和相对湿度(从100%到盐的风化值)的变化。利用单粒子腔衰荡光谱实现了折射率的精确和精确恢复。这种方法包括通过使用腔衰荡光谱和弹性光散射测量相结合的消光测量来探测被限制在贝塞尔激光束光学陷阱中的单个气溶胶粒子。此外，我们评估这些折射率测量的准确性，将我们的数据与以前报道的来自不同测量技术但在单一波长下的数据集进行比较。最后，我们给出了一个柯西色散模型，该模型将折射率测量参数化为波长和相对湿度。我们的参数应该为需要准确和全面地处理大气气溶胶无机成分折射率的波长和相对湿度依赖关系的研究人员提供有用的信息。
Calculations of aerosol radiative forcing require knowledge of wavelength-dependent aerosol optical properties, such as single-scattering albedo. These aerosol optical properties can be calculated using Mie theory from knowledge of the key microphysical properties of particle size and refractive index, assuming that atmospheric particles are well-approximated to be spherical and homogeneous. We provide refractive index determinations for aqueous aerosol particles containing the key atmospherically relevant inorganic solutes of NaCl, NaNO3, (NH4)(2)SO4, NH4HSO4 and Na2SO4, reporting the refractive index variation with both wavelength (400-650 nm) and relative humidity (from 100% to the efflorescence value of the salt). The accurate and precise retrieval of refractive index is performed using singleparticle cavity ring-down spectroscopy. This approach involves probing a single aerosol particle confined in a Bessel laser beam optical trap through a combination of extinction measurements using cavity ring-down spectroscopy and elastic light-scattering measurements. Further, we assess the accuracy of these refractive index measurements, comparing our data with previously reported data sets from different measurement techniques but at a single wavelength. Finally, we provide a Cauchy dispersion model that parameterises refractive index measurements in terms of both wavelength and relative humidity. Our parameterisations should provide useful information to researchers requiring an accurate and comprehensive treatment of the wavelength and relative humidity dependence of refractive index for the inorganic component of atmospheric aerosol.