Crystallization and Deliquescence of Atmospheric Particles

环境颗粒的相变将在现场使用1×3串联式差分迁移率分析仪与相对湿度的差分编程(“1×3 TDMA”)进行研究。这项研究将于2007年6月在俄克拉荷马州比林斯附近南部大平原(SGP)的美国能源部大气辐射测量(ARM)站点进行。将对三个可检验的假设进行初步评估。这些假设是基于实验室研究的结果，到目前为止，这些研究还没有对大气颗粒物进行测试。假设1：气溶胶潮解和结晶事件最常发生在化学中和程度较高的日子。为什么？实验室实验表明，酸性会降低结晶相对湿度(CRH)。此外，实验室结果还表明，足够酸性的颗粒是完全吸湿(不潮解)的。假设2：在累积模式中金属含量高的日子里，气溶胶CRH会移动得更高。相比之下，潮解相对湿度(DRH)将保持不变。这是因为金属及其氧化物可能是异质核，它们会增加CRH而不影响DRH。CRH值越高，意味着大气中结晶粒子出现的频率越高。假设3：经历相变的颗粒比例将随着TDMA测量中被识别为“更吸湿”的颗粒比例的增加而增加。这是因为“吸湿性较弱”的颗粒被认为是由煤烟和其他不溶解的有机分子组成的，这两个分子都不会经历RH调节的相变。该项目将首次展示一种在实验室外观测和量化大气气溶胶相变的新技术。所获得的数据将有助于确定气溶胶的潮解状态在大气辐射平衡中的重要性。该项目将为两名研究生提供研究机会。

The phase transitions of ambient particles will be studied in the field using a 1-by-3 Tandem Differential Mobility Analyzer with differential programming of relative humidity ("1-by-3 TDMA"). The study will take place during June 2007 at the DOE Atmospheric Radiation Measurement (ARM) site in the Southern Great Plains (SGP) near Billings, Oklahoma. Three testable hypotheses will be evaluated initially. The hypotheses are based upon the results of laboratory studies, which to date are untested for atmospheric particles. Hypothesis 1: Aerosol deliquescence and crystallization events will be observed most often on those days for which the degree of chemical neutralization is high. Why? Laboratory experiments show that acidity reduces crystallization relative humidity (CRH). Moreover, laboratory results also show that sufficiently acidic particles are fully hygroscopic (nondeliquescent). Hypothesis #2: Aerosol CRH's will be shifted higher on those days for which there is a high prevalence of metals in the accumulation mode. In contrast, the deliquescence relative humidities (DRH) will remain unchanged. The reason for this is that metals and their oxides are suspected heterogeneous nuclei, which increase CRH without affect DRH. Higher CRH values imply that crystalline particles occur more frequently in the atmosphere. Hypothesis #3: The fraction of particles undergoing phase transitions will increase in tandem with the fraction of particles identified as "more hygroscopic" in TDMA measurements. This is because the "less hygroscopic" particles are believed to be composed of soot and other non-dissolving organic molecules, neither of which undergo RH-regulated phase transitions. This project will provide the first demonstration of a novel technique to observe and quantify phase transitions of atmospheric aerosols outside the laboratory. The data obtained will help determine the importance of the deliquescence state of aerosols in the radiative balance of the atmosphere. The project will provide research opportunities of two graduate students.