Studies in Atmospheric Gas-to-Particle Conversion

9614105 Seinfeld该项目的目标是通过实验室实验、现场测量、成核理论和大气模型的综合计划，对大气成核和气体到颗粒的转化过程有一个基本的了解。将进行烟雾室实验，以研究含有大约7个或更多碳原子的碳氢化合物气相光氧化产生的气溶胶的产量。有些氧化产物具有足够低的蒸汽压，可以在气体和冷凝相之间分离，形成二次有机气溶胶。早期的实验解决了单一碳氢化合物在氮氧化物存在下的氧化；在这个项目中，将研究复杂的碳氢化合物混合物。这些将被选为受强烈人为影响的大陆大气的代表，以及偏远的、主要受生物因素支配的大陆大气的代表。为了更好地理解被认为是海洋边界层、自由对流层和被污染的大陆大气中新粒子最重要来源的硫酸/水体系的二元成核，将进行实验和模拟工作。实验将在光化学反应器中进行，目的是在一定的大气相关相对湿度范围内测量成核速率。此外，还将对离子诱导成核的一个简单模型进行蒙特卡罗模拟。将开发一种用于测量小气溶胶颗粒尺寸分布的差分迁移率分析仪（DMA），其充电系统将基于一个新概念：当DMA扫描颗粒尺寸范围时，它将通过改变离子密度来优化充电。对于较小的颗粒，可以施加较大的电荷，从而提高超细颗粒的计数效率，从而可以检测直径小于1nm的颗粒。该项目的另一个组成部分是参与北大西洋区域气溶胶特征试验（ACE-2），该试验将于1997年6月和7月在亚热带东北大西洋上空进行，是一项国际合作项目。ACE-2的主要目标是利用飞机、船载和地面测量，研究与辐射强迫和气候有关的大气气溶胶特性。通过这笔拨款，新的研究飞机“鹈鹕”将用于研究气溶胶的特性及其随时间的演变。对气溶胶大小分布和其他参数的测量将提供有关可能的新粒子产生和夹带、海洋上空云层对人为气溶胶的处理以及不同气团中云凝结核行为的信息。

9614105 Seinfeld The goal of this project is to develop a fundamental understanding of atmospheric nucleation and gas-to-particle conversion processes via an integrated program of laboratory experiments, field measurements, nucleation theory, and atmospheric modeling. Smog chamber experiments will be performed to study the yields of aerosols from the gas-phase photooxidation of hydrocarbons containing roughly seven or more carbon atoms. Some of the oxidation products have sufficiently low vapor pressures to partition between the gas and the condensed phase, forming secondary organic aerosols. Earlier experiments addressed the oxidation of single hydrocarbons in the presence of nitrogen oxides; in this project, complex hydrocarbon mixtures will be investigated. These will be chosen to be representative of the strongly anthropogenically-influenced continental atmosphere as well as the remote, largely biogenically-dominated, continental atmosphere. Experiments and modeling work will be performed in order to better understand binary nucleation of the sulfuric acid/water system, which is regarded as the most important source of new particles in the marine boundary layer, the free troposphere, and the polluted continental atmosphere. The experiments will be conducted in a photochemical reactor with the goal of measuring the rate of nucleation over a range of atmospherically relevant relative humidities. In addition, Monte Carlo simulations of a simple model for ion-induced nucleation will be carried out. A Differential Mobility Analyzer (DMA) for measuring the size distribution of small aerosol particles will be developed whose charging system will be based on a new concept: it will optimize the charging by varying the ion density as the particle size range is scanned by the DMA. It will be possible to apply larger charges for the smaller particles and therefore enhance the counting efficiency for ultrafine particles, allowing detection of particles whose diameter is below 1 nm. Another component of this project is the participation in the North Atlantic Regional Aerosol Characterization Experiment (ACE-2) which will be conducted in June and July, 1997, over the subtropical Northeastern Atlantic Ocean as an international collaborative effort. The main objectives of ACE-2 are to study the properties of atmospheric aerosols relevant to radiative forcing and climate using aircraft, ship-board, and ground-based measurements. Through this grant, the new research aircraft Pelican will be deployed to investigate aerosol properties and their evolution in time. Measurements of aerosol size distributions and other parameters will provide information on possible new particle production and entrainment, processing of anthropogenic aerosol by clouds over the ocean, and the behavior of cloud condensation nuclei in different air masses.