Particle Nucleation Events in the Ohio River Valley

将获得和分析俄亥俄州河谷森林中超细颗粒的时间序列，以量化成核事件和高超细颗粒浓度的频率和特征，包括化学成分、成核的主要机制以及成核和生长的限制。 目前的数值模型将评估其预测成核和随后的颗粒生长的发生的能力。 具体的研究假设包括：1）尽管平均凝结汇相对较高，但至少有10%的天数会观测到成核事件，其中春季的成核事件数量最多; 2）以高超细粒子浓度为特征的成核事件的空间范围为数十至数百公里; 3）成核作用发生在森林冠层上方，生成的颗粒物随后被输送到冠层中并穿过冠层; 4）在该位置成核的主要机制是H_2SO_4-H_2 O-NH_3三元成核（硫酸、水、氨）; 5）随后的颗粒生长主要是通过添加由生物和人为有机化合物氧化形成的半挥发性有机物; 6）成核的主要物理控制是现有的颗粒表面积（如通过冷凝汇所显示的）和紫外辐射通量;和7）成核的主要化学控制是NH3的可用性。研究的更广泛的科学影响包括与其他长期数据集进行比较分析，以量化共性和差异，以及验证和开发用于全球大气化学和气候模型的大气边界层成核预测模型所需的信息。 更广泛的影响还包括研究生和本科生的教育和培训。

A time series of ultra-fine particles in a forest in the Ohio River Valley will be acquired and analyzed to quantify the frequency and characteristics of nucleation events and high ultra-fine particle concentrations, including chemical composition, principal mechanisms of nucleation, and limitations on nucleation and growth. Current numerical models will be assessed for their ability to predict the occurrence of nucleation and subsequent particle growth. Specific research hypotheses to be tested include: 1) Despite a relatively high average condensational sink, nucleation events will be observed on at least 10% of days, with the highest number occurring in spring; 2) The spatial extent of events characterized by high ultra-fine particle concentrations is of the order of tens to hundreds of kilometers; 3) Nucleation occurs above the forest canopy and the resulting particles are subsequently transported into and through the canopy; 4) The principal mechanism of nucleation at this location is ternary nucleation of H2SO4-H2O-NH3 (sulfuric acid, water, ammonia); 5) Subsequent particle growth is principally by addition of semi-volatile organics formed from oxidation of biogenic and anthropogenic organic compounds; 6) The major physical controls on nucleation are existing particle surface area (as manifest through the condensational sink) and UV radiative flux; and 7) The major chemical control on nucleation is NH3 availability.Broader scientific impacts of the research include comparative analyses with other long-term data sets to quantify commonalities and differences, and information necessary to validate and develop predictive models of nucleation in the atmospheric boundary layer for use in global atmospheric chemistry and climate models. The broader impacts also include education and training of graduate and undergraduate students.