| 16834200 |
Wagner R, Naumann KH, Mangold A, Mohler O, Saathoff H, Schurath U: Aerosol chamber study of optical constants and N2O5 uptake on supercooled H2SO4/H2O/HNO3 solution droplets at polar stratospheric cloud temperatures. J Phys Chem A. 2005 Sep 15;109(36):8140-8.
The mechanism of the formation of supercooled ternary H (2) SO (4)/H (2) O/HNO (3) solution (STS) droplets in the polar winter stratosphere, i.e., the uptake of nitric acid and water onto background sulfate aerosols at T < 195 K, was successfully mimicked during a simulation experiment at the large coolable aerosol chamber AIDA of Forschungszentrum Karlsruhe. Supercooled sulfuric acid droplets, acting as background aerosol, were added to the cooled AIDA vessel at T = 193.6 K, followed by the addition of ozone and nitrogen dioxide. N (2) O (5), the product of the gas phase reaction between O (3) and NO (2), was then hydrolyzed in the liquid phase with an uptake coefficient gamma (N (2) O (5)). From this experiment, a series of FTIR extinction spectra of STS droplets was obtained, covering a broad range of different STS compositions. This infrared spectra sequence was used for a quantitative test of the accuracy of published infrared optical constants for STS aerosols, needed, for example, as input in remote sensing applications. The present findings indicate that the implementation of a mixing rule approach, i.e., calculating the refractive indices of ternary H (2) SO (4)/H (2) O/HNO (3) solution droplets based on accurate reference data sets for the two binary H (2) SO (4)/H (2) O and HNO (3)/H (2) O systems, is justified. Additional model calculations revealed that the uptake coefficient gamma (N (2) O (5)) on STS aerosols strongly decreases with increasing nitrate concentration in the particles, demonstrating that this so-called nitrate effect, already well-established from uptake experiments conducted at room temperature, is also dominant at stratospheric temperatures. |
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