Gas-Particle Transport Limitations in Atmospheric Aerosols

ATM-9422993约翰斯顿在这个项目中，将调查两个与对流层空气污染中的气粒输送有关的区域。第一个假设是有机化合物的表面涂层限制了颗粒的凝结和蒸发。特别是，氨对硫酸颗粒的呼吸和大气中和作用可能会被大气有机物的表面涂层所抑制。为了验证这一假设，含有表面活性有机物的硫酸颗粒将暴露在氨蒸气中。氨对硫酸的调节系数将作为有机涂层的组成和厚度的函数来确定。第二个假设是，颗粒形态，即当水颗粒干燥时形成的固相，可能会抑制挥发性成分的蒸发或冷凝。特别是，将研究与受污染的城市环境有关的硝酸铵/硫酸铵颗粒物。如果干燥时形成硫酸铵表面涂层，则硝酸铵的蒸发将被抑制。为了验证这一假设，含有硝酸铵和硫酸铵的水颗粒将被干燥，并对干燥颗粒的形态进行表征。以这种方式产生和表征的颗粒的蒸发速率将被测量。这项研究的大部分将使用快速单粒子质谱仪(RSMS)进行，这是一种在线分析单个气溶胶粒子的新方法，是由美国国家科学基金会先前资助开发的。样品粒子通过连续激光束的光散射检测，然后被脉冲准分子束烧蚀。用飞行时间质谱仪检测激光解吸/电离产生的离子，并根据离子的分布推断粒子的化学组成。

ATM-9422993 Johnston In this project, two areas that are relevant to gas-particle transport in tropospheric air pollution will be investigated. The first hypothesis is that surface coatings of organic compounds limit condensation and evaporation of particles. In particular, respiratory and atmospheric neutralization of sulfuric acid particles by ammonia may be inhibited by surface coatings of atmospheric organic matter. To test this hypothesis, sulfuric acid particles containing surface active organics will be exposed to ammonia vapor. The accommodation coefficient of ammonia onto sulfuric acid will be determined as a function of the composition and thickness of the organic coating. The second hypothesis is that particle morphology, namely formation of solid phases as an aqueous particle dries, may inhibit evaporation or condensation of volatile components. In particular, ammonium nitrate/ammonium sulfate particles relevant to polluted urban environments will be studied. If an ammonium sulfate surface coating forms upon drying, then evaporation of ammonium nitrate will be inhibited. To test this hypothesis, aqueous particles containing ammonium nitrate and ammonium sulfate will be dried and the morphology of the dry particles will be characterized. The evaporation rates of particles generated and characterized in this manner will be measured. Most of this research will be performed with rapid-single particle mass spectrometry (RSMS), a new method for on-line chemical analysis of single aerosol particles that was developed with previous NSF funding. The sample particles are detected by light scattering from a continuous laser beam and then ablated by a pulsed excimer beam. Ions produced by laser desorption/ionization are detected by time-of-flight mass spectrometry and the chemical composition of the particles is inferred by the distribution of ions o`served.