Experimental study of the role of physicochemical surface processing on the IN ability of mineral dust particles
Experimental study of the role of physicochemical surface processing on the IN ability of mineral dust particles
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DOI：
10.5194/acp-11-11131-2011
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发表时间：
2011-11
影响因子：
6.3
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中科院分区：
文献类型：
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抽象的。利用莱比锡气溶胶云相互作用模拟器(LACIS)，研究了在浮冰模式下，不同表面改性对亚利桑那州试验尘埃(ATD)粒子成冰能力的影响。将粉尘颗粒暴露在硫酸蒸气、水蒸气中以及添加和不添加氨气的情况下，并使用在250°C下操作的热传感器进行加热。选定的尺寸将迁移率直径为300 nm的准单分散颗粒送入LACI，并在这些颗粒上生长液滴，使每个液滴包含一个颗粒。在−40°C≤T≤−28°C的温度范围内测定了这些液滴随温度变化的冻结分数。纯ATD粒子在很宽的温度范围内成核冰，它们的冻结行为被分成两个冻结分支，其特征是冻结分数-温度曲线的斜率不同。硫酸包覆后，颗粒的IN电位在第一个冻结支链(T&gT；−35°C)显著降低，在第二个支链(T≤−35°C)略有升高。硫酸包衣后加入水蒸气，导致第一冻结枝消失，第二冻结枝的IN能力大大降低。与水蒸气的影响相比，水蒸气暴露期间氨气的存在对颗粒的IN能力的影响可以忽略不计。在热介质中加热导致两个支链的硫酸包覆粒子的IN能力降低，但附加的加热不改变或仅轻微改变纯ATD和水蒸气暴露的硫酸包覆粒子的IN能力。换句话说，硫酸和水蒸气的结合是ATD颗粒冰活性表面特征被破坏的主要原因。一个可能的解释是冰活性金属硅酸盐向金属硫酸盐的化学转化。在有水蒸气存在的情况下，硫酸与尘埃之间的反应强烈增强，从而显著降低了IN势，这对大气冰云的形成是重要的。我们的研究结果表明，在所研究的条件下，IN浓度最多可以降低一个数量级。
Abstract. During the measurement campaign FROST 2 (FReezing Of duST 2), the Leipzig Aerosol Cloud Interaction Simulator (LACIS) was used to investigate the influence of various surface modifications on the ice nucleating ability of Arizona Test Dust (ATD) particles in the immersion freezing mode. The dust particles were exposed to sulfuric acid vapor, to water vapor with and without the addition of ammonia gas, and heat using a thermodenuder operating at 250 °C. Size selected, quasi monodisperse particles with a mobility diameter of 300 nm were fed into LACIS and droplets grew on these particles such that each droplet contained a single particle. Temperature dependent frozen fractions of these droplets were determined in a temperature range between −40 °C ≤ T ≤−28 °C. The pure ATD particles nucleated ice over a broad temperature range with their freezing behavior being separated into two freezing branches characterized through different slopes in the frozen fraction vs. temperature curves. Coating the ATD particles with sulfuric acid resulted in the particles' IN potential significantly decreasing in the first freezing branch ( T >−35 °C) and a slight increase in the second branch ( T ≤−35 °C). The addition of water vapor after the sulfuric acid coating caused the disappearance of the first freezing branch and a strong reduction of the IN ability in the second freezing branch. The presence of ammonia gas during water vapor exposure had a negligible effect on the particles' IN ability compared to the effect of water vapor. Heating in the thermodenuder led to a decreased IN ability of the sulfuric acid coated particles for both branches but the additional heat did not or only slightly change the IN ability of the pure ATD and the water vapor exposed sulfuric acid coated particles. In other words, the combination of both sulfuric acid and water vapor being present is a main cause for the ice active surface features of the ATD particles being destroyed. A possible explanation could be the chemical transformation of ice active metal silicates to metal sulfates. The strongly enhanced reaction between sulfuric acid and dust in the presence of water vapor and the resulting significant reductions in IN potential are of importance for atmospheric ice cloud formation. Our findings suggest that the IN concentration can decrease by up to one order of magnitude for the conditions investigated.