New Particle Formation Experiments: Nucleation and Growth

这个项目的重点是大气中新粒子的形成和生长。将进行实验室实验，以测量新颗粒的形成和生长速度随成分、温度和相对湿度的变化。这些结果有望提高预测新颗粒形成对气候、健康和能见度的影响的准确性。实验室研究包括以下实验：(1)测量作为试剂浓度和温度的函数的氨-H_2SO_4体系的成核率；(2)在低H_2SO_4浓度下测量氨对胺-H_2SO_4体系的成核率的协同效应；(3)使用光解流动反应器表征生长速度，并使用在气相中注入生长剂的第二流动反应器；(4)测量选定有机化合物的生长能力的纳米颗粒尺寸依赖关系；(5)通过将测量的气相浓度纳入模型模拟来估计绝对增长率(即吸收效率)；以及(6)探索光解流动反应器作为工具的能力，以通过吸收复杂的二次氧化产物来理解生长，例如在α-Pinen的光氧化中产生的。首席调查员(PI)计划使用流动反应器的计算流体动力学(CFD)模拟来支持对实验结果的解释。CFD模拟允许估计小分子团簇的自由能，并将结果外推到其他实验中的条件，以便可以比较成核速率。PI打算将这个项目的结果与CERN云项目的全球大气粒子形成测量结果进行比较。该项目将通过让本科生接触高水平的实验和计算工作，为他们在科学领域的职业生涯做准备，从而帮助培养本科生的研究能力。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 formation and growth of new particles in the atmosphere. Laboratory experiments will be conducted to measure changes in the rate of new particle formation and growth with changes in composition, temperature, and relative humidity. The results are expected to lead to improved accuracy in predicting the impacts of new particle formation on climate, health and visibility.Laboratory research includes experiments to: (1) conduct measurements of nucleation rates in the ammonia - H2SO4 system as a function of reagent concentrations and temperature; (2) conduct measurements of the synergistic effect of ammonia on nucleation rates for the amine - H2SO4 system at low H2SO4 concentrations; (3) characterize growth rates using a Photolytic Flow Reactor with growth via H2SO4 and using a second flow reactor with growth agents injected in the vapor phase; (4) measure the nanoparticle size-dependency of the growth capabilities of select organic compounds; (5) estimate absolute growth rates (i.e., uptake efficiency) by incorporating measured gas-phase concentrations into model simulations; and (6) explore the capability of the Photolytic Flow Reactor as a tool for understanding growth via uptake of complex secondary oxidation products such as are produced in photo-oxidation of alpha-pinene.The Principal Investigator (PI) plans to use computational fluid dynamics (CFD) simulations of the flow reactor to bolster the interpretation of the experimental results. The CFD simulations allow for estimates of the free energies of small molecular clusters and extrapolations of the results to conditions in other experiments so that nucleation rates can be compared. The PI intends to compare the results from this project with global atmospheric particle formation measurements from the CERN CLOUD project.The project will help develop undergraduate research capabilities by exposing undergraduates to high-level experimental and computational work that will prepare them for careers in science.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.