Effect of Water and Acidity on Formation of Secondary Organic Aerosol

该项目支持对水在二次有机气溶胶（SOA）形成中的作用进行全面研究。SOA的形成是由于挥发性有机化合物的大气氧化，导致在气相和颗粒相之间分配的产物。观测到的有机气溶胶的大气水平，其中占主导地位的是SOA，超过目前的模式预测。水在大气颗粒物中无处不在，但气溶胶水在有机物气-粒分配和颗粒相化学中的作用尚不清楚。该项目将包括：（1）无机-有机气溶胶系统的相行为和气-粒分配的严格模型的应用;（2）对挥发性有机化合物（VOCs）的全谱进行实验室研究，旨在揭示水在气-粒分配和SOA形成中的非均相化学中的机制和重要性;以及（3）分析环境数据中颗粒相化学和酸度在确定SOA形成中的作用。热力学模拟将应用于：（1）人工的、定义明确的有机-无机混合物;（2）受控气溶胶室实验;和（3）环境数据。 实验室研究计划的总体目标是全面解决相对湿度（RH），气溶胶酸度和颗粒相化学对SOA形成的影响。 进行的实验将涉及：（1）挥发性有机化合物的全谱;（2）氮氧化物（NOx）的高低水平;（3）种子气溶胶酸度的变化;以及（4）相对湿度的变化。 这些包括有机气溶胶老化的机制，导致大气中发现的高度氧化状态。 在实验室室研究中，将确定颗粒相化学和酸性增强SOA形成的独特标记化合物。评估这些化合物在环境气溶胶样品中的存在程度，可以揭示是否有可能辨别有机碳的来源，气溶胶“年龄”向其均匀化，高度氧化的状态。这项工作将有助于提高我们的知识，对气候敏感性的理解大气气溶胶的辐射强迫。 气溶胶辐射强迫直接取决于大气中气溶胶的质量。 有机气溶胶约占全球气溶胶质量的一半，而多达90%的有机气溶胶质量是由于挥发性有机化合物的气相氧化而形成的。 将向社会提供将要开发的气溶胶成分模型和将要获得的实验室数据。学生将接受该项目的培训，所有学生都将参加科学会议，介绍他们的研究成果，这些成果也将发表在同行评审的期刊上。

This project supports a comprehensive study of the role of water in the formation of secondary organic aerosol (SOA). SOA forms as a result of atmospheric oxidation of volatile organic compounds, leading to products that partition between the gas and particle phases. Observed atmospheric levels of organic aerosol, of which the preponderance is SOA, exceed those predicted by current models. Water is ubiquitous in atmospheric particles, but the role of aerosol water in the gas-particle partitioning of organics and in particle-phase chemistry is unclear. The project will include: (1) application of a rigorous model of the phase behavior and gas-particle partitioning of inorganic-organic aerosol systems; (2) laboratory chamber studies with a full spectrum of volatile organic compounds (VOCs) designed to reveal the mechanism and importance of water in gas-particle partitioning and heterogeneous chemistry in SOA formation; and (3) analysis of ambient data with respect to the role of particle-phase chemistry and acidity in determining SOA formation.Thermodynamic modeling will be applied to: (1) artificial, well-defined organic-inorganic mixtures; (2) controlled aerosol chamber experiments; and (3) ambient data. The overall goal of the experimental chamber research program is to address comprehensively the effects of relative humidity (RH), aerosol acidity, and particle-phase chemistry on SOA formation. The experiments to be conducted will involve: (1) a full spectrum of VOCs; (2) high and low nitrogen oxide (NOx) levels; (3) variation of seed aerosol acidity; and (4) variation of RH. These include mechanisms of organic aerosol aging that lead to the highly oxidized state found in the atmosphere. In the laboratory chamber studies, unique marker compounds for both particulate-phase chemistry and acidity-enhanced SOA formation will be identified. Evaluation of the extent to which such compounds are present in ambient aerosol samples can shed light on the question of whether it is possible to discern the sources of organic carbon as the aerosol "ages" toward its homogenized, highly oxidized state.This work will contribute to understanding of climate sensitivity by improving our knowledge of the radiative forcing of atmospheric aerosols. Aerosol radiative forcing depends directly on the mass of aerosols in the atmosphere. Organic aerosols comprise roughly one-half of the global aerosol mass, and as much as 90% of the organic aerosol mass is formed as a result of the gas-phase oxidation of volatile organic compounds. The model of aerosol composition to be developed and the laboratory data to be obtained will be made available to the community.A postdoctoral scholar and two Ph.D. students will be trained in the project, all of whom will attend scientific conferences to present their research results, which will also be published in peer-reviewed journals.