| 1. |
- Bilde, M., et al.
(author)
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Saturation Vapor Pressures and Transition Enthalpies of Low-Volatility Organic Molecules of Atmospheric Relevance: From Dicarboxylic Acids to Complex Mixtures
- 2015
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In: Chemical Reviews. - : American Chemical Society (ACS). - 0009-2665 .- 1520-6890. ; 115:10, s. 4115-4156
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Research review (peer-reviewed)abstract
- There are a number of techniques that can be used that differ in terms of whether they fundamentally probe the equilibrium and the temperature range over which they can be applied. The series of homologous, straight-chain dicarboxylic acids have received much attention over the past decade given their atmospheric relevance, commercial availability, and low saturation vapor pressures, thus making them ideal test compounds. Uncertainties in the solid-state saturation vapor pressures obtained from individual methodologies are typically on the order of 50-100%, but the differences between saturation vapor pressures obtained with different methods are approximately 1-4 orders of magnitude, with the spread tending to increase as the saturation vapor pressure decreases. Some of the dicarboxylic acids can exist with multiple solid-state structures that have distinct saturation vapor pressures. Furthermore, the samples on which measurements are performed may actually exist as amorphous subcooled liquids rather than solid crystalline compounds, again with consequences for the measured saturation vapor pressures, since the subcooled liquid phase will have a higher saturation vapor pressure than the crystalline solid phase. Compounds with equilibrium vapor pressures in this range will exhibit the greatest sensitivities in terms of their gas to particle partitioning to uncertainties in their saturation vapor pressures, with consequent impacts on the ability of explicit and semiexplicit chemical models to simulate secondary organic aerosol formation.
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| 2. |
- Hoyle, C. R., et al.
(author)
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Ice nucleation properties of volcanic ash from Eyjafjallajokull
- 2011
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In: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 11:18, s. 9911-9926
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Journal article (peer-reviewed)abstract
- The ice nucleation ability of volcanic ash particles collected close to the Icelandic volcano Eyjafjallajokull during its eruptions in April and May 2010 is investigated experimentally, in the immersion and deposition modes, and applied to atmospheric conditions by comparison with airborne measurements and microphysical model calculations. The number of ash particles which are active as ice nuclei (IN) is strongly temperature dependent, with a very small minority being active in the immersion mode at temperatures of 250-263 K. Average ash particles show only a moderate effect on ice nucleation, by inducing freezing at temperatures between 236K and 240K (i.e. approximately 3-4K higher than temperatures required for homogeneous ice nucleation, measured with the same instrument). By scaling the results to aircraft and lidar measurements of the conditions in the ash plume days down wind of the eruption, and by applying a simple microphysical model, it was found that the IN active in the immersion mode in the range 250-263K generally occurred in atmospheric number densities at the lower end of those required to have an impact on ice cloud formation. However, 3-4K above the homogeneous freezing point, immersion mode IN number densities a few days down wind of the eruption were sufficiently high to have a moderate influence on ice cloud formation. The efficiency of IN in the deposition mode was found to be poor except at very cold conditions (<238 K), when they reach an efficiency similar to that of mineral dust with the onset of freezing at 10% supersaturation with respect to ice, and with the frozen fraction nearing its maximum value at a supersaturation 20%. In summary, these investigations suggest volcanic ash particles to have only moderate effects on atmospheric ice formation.
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