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.
Under this proposal, the Whole Air Sample Profiler (WASP) was designed to collect a continuous air sample over a discrete period of time in a long, narrow tube. The resulting air sample provides a cross section in space. Once collected, WASP is returned to the laboratory for subsequent analysis using an appropriate analytical technique. WASP is an aircraft based system. It is comprised of a long coiled tube into which sample air is flowed. The air sample is collected during flight, and returned to the laboratory for subsequent analysis. Sample collection time is dependent upon air flow and tube length. Under this proposal, WASP was deployed out of Colorado Springs during July 2011. Approximately 32 vertical profiles were collected over 7 flight days, from an altitude of approximately 100m to 800m above the ground. Profiles were collected over three discrete areas: Black Forest, predominantly Pine; Palmer Divide, an Oak stand; and Manitou Forest, predominantly pine. The latter location was where the 2010 and 2011 BEACHON (Biosphere-Atmosphere Exchange of Aerosol within Cloud, Carbon, and Hydrologic Cycles including Organics and Nitrogen) summer research intensives were located. Sample collection time was on the order of 60 seconds, during which time the research aircraft climbed rapidly from approximately 100 meters above the ground to 800 meters. Results show the WASP operates well and trace gas profiles can indeed be measured with a vertical resolution more than ten times greater than that measured from balloons.