RAPID: A New Technique for Vertical Profiling of Volatile Organic Compounds Within and Above the Convective Boundary Layer

挥发性有机化合物（VOCs）对森林冠层化学和氧化电位的主导作用是众所周知的。但是，如果不知道VOCs的浓度垂直分布，就不能很精确地计算其通量。延伸到冠层高度以上的垂直剖面通常由气球采样确定，但由于气球平台固有的限制，只能在一个或两个不同的高度采集样本，在每个高度采集样本需要花费许多分钟，而且气球剖面很少能够接近对流边界层（CBL）的顶部，因此通常只能观测到部分剖面。这个RAPID项目将在2011年夏季的BEACHON（生物圈-大气能量、气溶胶、碳、水、有机物和氮交换）密集采样活动期间及时开发，这是一项从小型研究飞机上收集CBL内和覆盖较低自由对流层的VOCs垂直剖面的技术。这项技术被称为“冷冻取样”，原理很简单；轻型飞机内装有一根比较长的空气管。在快速爬升过程中，样品空气流过油管。当样品到达垂直剖面的上端时，通过阀门关闭两端，样品被困住或“冻结”在油管内。在很短的时间内（大约一分钟），一个垂直剖面被困在样品管中，并储存起来，直到样品可以在地面上分析。“冻结取样”技术将对许多地面野外活动有用，在这些活动中需要低水平、高分辨率的垂直剖面。此外，两名本科生将参与确定采样系统的特性，运用他们的流体动力学、化学和物理知识在现实世界中的应用。学生们还将前往科罗拉多州的马尼托森林，协助BEACHON活动的实地组成部分。至少有一名学生将从石溪大学的WISE（女性科学与工程）项目中招募。

The dominating role of volatile organic compounds (VOCs) on the chemistry and oxidation potential within a forest canopy is well known. However, without knowing the concentration vertical profiles of VOCs, one cannot calculate their flux with much precision. Vertical profiles extending above the canopy height are usually determined by sampling from balloons but because of limitations inherent to balloon platforms, samples can only be taken at one or two different altitudes, it takes many minutes to collect a sample at each altitude, and balloon profiles rarely are able to get near the top of the convective boundary layer (CBL), thus only a partial profile is usually observable. This RAPID project will develop in time for initial deployment during the BEACHON (Biosphere-atmosphere Exchange of Energy, Aerosols, Carbon, H2O, Organics & Nitrogen) intensive sampling campaign in summer 2011 a technique to collect vertical profiles of VOCs within the CBL and overlying lower free troposphere from a small research aircraft. The technique, called "frozen sampling", is simple in principle; a relatively long tube of air is installed within a light aircraft. During a rapid climb, sample air flows through the tubing. Upon reaching the upper point of the vertical profile, the sample is trapped or "frozen" within the tubing by closing off both ends, using valves. Within a very short period of time (on the order of one minute) a vertical profile is trapped within the sample tubing, and stored until the sample can be analyzed on the ground.The "frozen sampling" technique will be useful to many ground-based field campaigns, where low level, high resolution vertical profiles are desirable. In addition, two undergraduate students will be involved in determining the characteristics of the sampling system, using their knowledge of fluid dynamics, chemistry, and physics in a real world application. The students will also travel to Manitou Forest in Colorado and assist with the field component of the BEACHON campaign. At least one of the students will be recruited from the WISE (Women in Science and Engineering) Program at Stony Brook University.