Understanding Formation of Condensible Organics from Photochemical Oxidation During New-Particle Formation Experiments

该项目的重点是研究大气中新粒子的形成和生长。这项研究将结合欧洲核子研究中心的合作实验，作为宇宙离开室外水滴(云)联盟的一部分，与卡内基梅隆大学(CMU)的烟雾室研究相结合。云实验设备可能是世界上最复杂的关于大气新粒子形成的实验。在云中，CMU团队将使用碘化学电离质谱仪来测量气体和不断增长的颗粒的组成，后者通过从特氟龙过滤器(FIGAERO CIMS)热解吸来测量。主要目标将是了解气相氧化化学如何使产品具有极低的蒸汽压，能够形成新的颗粒，并冷凝在现有颗粒上使其生长。一个主要的关注点将是将云中的化学条件与传统雾霾室内实验中的化学条件进行比较，前者更接近于干净的背景大气，后者往往超过污染最严重的城市。该项目将侧重于过氧基的形成和随后可将半挥发性过氧基转化为低挥发性过氧基的“自动氧化”的作用，以及随后产生可缩合产物的终止化学。这项研究将构成两篇学生论文的核心。其中一个将主要集中在气相氧化化学上，特别是高度氧化的过氧基的来源和去向与温度有关，这些过氧基被认为是低挥发性和极低挥发性有机化合物形成的中心。另一个重点是凝聚相的组成和半挥发性有机化合物的反应性吸收促进颗粒生长的潜力。该项目的结果将使人们更好地了解与新粒子形成和生长相关的限速基本步骤，以及可能干扰这些限速步骤的相互竞争的大气过程。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This project focuses on the study of the formation and growth of new particles in the atmosphere. The research will combine collaborative experiments at CERN as part of the Cosmics Leaving OUtdoor Droplets (CLOUD) consortium, with smog-chamber studies at Carnegie Mellon University (CMU). The CLOUD experimental facility is likely the world's most sophisticated experiment addressing atmospheric new-particle formation. It was constructed to measure new particle formation under highly controlled, ultra-clean conditions.At CLOUD, the CMU team will use an iodide chemical ionization mass spectrometer to measure the composition of gases and growing particles, the later by thermal desorption from teflon filters (FIGAERO CIMS). The major objective will be to understand how gas-phase oxidation chemistry makes products with extraordinary low vapor pressures, capable of forming new particles and also condensing on existing particles making them grow. A major focus will be to compare chemical conditions in CLOUD, which more closely resemble the clean background atmosphere, with those in traditional smog chamber experiments, that often exceed those in the most polluted cities. The project will focus on the role of peroxy radical formation and subsequent "auto-oxidation" that can convert semi-volatile peroxy radicals into low-volatility peroxy radicals, and the subsequent termination chemistry that generates condensible products.This research will form the core of two student dissertations. One will focus principally on gas-phase oxidation chemistry, specifically the temperature dependent sources and fate of highly oxidized peroxy radicals that is hypothesized to be at the center of the formation of low-volatility and extremely low-volatility organic compounds. The other will focus on the composition of the condensed phase and the potential for reactive uptake of semivolatile organic compounds to contribute to particle growth. The project results will yield a much better understanding of the rate-limiting elementary steps associated with new-particle formation and growth and competing atmospheric processes that might interfere with those rate-limiting steps.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.