Comparison of the Accuracy of Aerosol Refractive Index Measurements from Single Particle and Ensemble Techniques

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• 作者：Bernard J. Mason ; Simon-John King ; Rachael E. H. Miles ; Katherine M. Manfred ; Andrew M. J. Rickards ; Jin Kim ; Jonathan P. Reid ; Andrew J. Orr-Ewing
• 刊名：The Journal of Physical Chemistry A
• 出版年：2012
• 出版时间：August 23, 2012
• 年：2012
• 卷：116
• 期：33
• 页码：8547-8556
• 全文大小：403K
• 年卷期：v.116,no.33(August 23, 2012)
• ISSN：1520-5215

文摘

The ability of two techniques, aerosol cavity ring down spectroscopy (A-CRDS) and optical tweezers, to retrieve the refractive index of atmospherically relevant aerosol was compared through analysis of supersaturated sodium nitrate at a range of relative humidities. Accumulation mode particles in the diameter range 300鈥?00 nm were probed using A-CRDS, with optical tweezer measurements performed on coarse mode particles several micrometers in diameter. A correction for doubly charged particles was applied in the A-CRDS measurements. Both techniques were found to retrieve refractive indices in good agreement with previously published results from Tang and Munkelwitz, with a precision of 卤0.0012 for the optical tweezers and 卤0.02 for the A-CRDS technique. The coarse mode optical tweezer measurements agreed most closely with refractive index predictions made using a mass-weighted linear mixing rule. The uncertainty in the refractive index retrieved by the A-CRDS technique prevented discrimination between predictions using both mass-weighted and volume-weighted linear mixing rules. No efflorescence or kinetic limitations on water transport between the particle and the gas phase were observed at relative humidities down to 14%. The magnitude of the uncertainty in refractive index retrieved using the A-CRDS technique reflects the challenges in determining particle optical properties in the accumulation mode, where the extinction efficiency varies steeply with particle size.