Crystallization and Deliquescence of Atmospheric Particles

将使用具有相对湿度差分编程的 1×3 串联差分迁移率分析仪（“1×3 TDMA”）在现场研究环境颗粒的相变。 该研究将于 2007 年 6 月在俄克拉荷马州比林斯附近的南部大平原 (SGP) 的能源部大气辐射测量 (ARM) 站点进行。 最初将评估三个可检验的假设。 这些假设是基于实验室研究的结果，迄今为止尚未对大气颗粒进行测试。 假设1：气溶胶潮解和结晶事件最常在化学中和程度高的日子观察到。 为什么？ 实验室实验表明，酸度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的（不潮解）。 假设#2：在金属积累模式盛行的那些日子里，气溶胶 CRH 将会升高。 相反，潮解相对湿度（DRH）将保持不变。 其原因是金属及其氧化物被怀疑是异质核，它们会增加CRH而不影响DRH。 CRH 值越高意味着大气中结晶颗粒出现的频率越高。 假设#3：经历相变的颗粒比例将与 TDMA 测量中被识别为“更吸湿”的颗粒比例同时增加。 这是因为“吸湿性较小”的颗粒被认为是由烟灰和其他不溶解的有机分子组成，它们都不会经历相对湿度调节的相变。 该项目将首次演示一种在实验室外观察和量化大气气溶胶相变的新技术。 获得的数据将有助于确定气溶胶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.