Atmospheric Tracer Technology Providing Ground Truth for Dispersion and Air Quality Monitoring Understanding how the atmosphere transports and disperses materials released into the air is essential to understanding and dealing with important problems such as air pollution and accidental (or intentional) toxic gas releases. FRD's atmospheric tracer experiments improve our understanding by providing basic information about transport and dispersion processes. An atmospheric tracer experiment is conceptually very simple. A small amount of stable, non-toxic, invisible, odorless, and easily detectable substance (known as a tracer) is released into the air. The air in the surrounding area is sampled and the concentration of the tracer is measured. By combining the tracer concentrations with meteorological information, scientists can develop and test theories and models of atmospheric transport and dispersion. The FRD is a pioneer in the use of gaseous atmospheric tracers. In the mid 1960's, we pioneered the use of gas chromatography with electron capture detectors to analyze air samples for the atmospheric tracer sulfur hexafluoride (SF6). Since then, we have developed and refined air sampling and analytical techniques for SF6 and other intentionally released atmospheric tracers, and we have participated in tracer experiments on local, regional, national, and international scales. Our current capabilities include continuous (near real time) analyzers, time integrated sampling, and automated tracer release mechanisms.

FRD is a pioneer in atmospheric tracer experiments dating back to the 1960's. Our recent work has expanded to include studies important to national security and dispersion of toxic agents during a terrorist attack.

Real Time SF6 Analyzers The real time sulfur hexafluoride SF6 analyzers are vehicle or lab cart mounted systems that make measurements of atmospheric SF6 concentrations with a response time of just under one second. The rapid response time and mobility of the analyzers suit them ideally for measurements of plume widths and structure. They have been utilized in experiments measuring both across wind and along wind diffusion parameters commonly used in Gaussian plume transport and dispersion models. The real time SF6 analyzers include a computer controlled calibration system and an integrated global positioning system (GPS) that tags each data point with sampling time and location. Run time quality control (QC) outputs allow operators to monitor system performance. The system has been used in cars, boats, aircraft, and buildings. The current configuration easily sits in car or aircraft passenger seats and attaches with standard seat belts. (details)

FRD's real time sampling system is easily carried in the back seat of an SUV.

Time Integrated Sampling This sampling system provides average tracer concentrations over specific time intervals at specific sampling locations. Typically, the Programmable Integrating Gas Samplers (PIGS) are placed at pre-selected points prior to the start of the experiment and programmed to collect samples over the period of the experiment. The PIGS collect 12 samples each by pumping air into Tedlar bags. After the experiment is over, the samples are collected and analyzed with the Automated Tracer Gas Analysis System (ATGAS). Sample bags are typically exchanged in the PIGS so sampling can continue while the analysis takes place. By placing a relatively large number of PIGS (we currently have about 100) on a grid across the experimental area, a good footprint of the tracer plume can be determined for each sampling period. The system allows many simultaneous measurements to be made and also offers the advantage of easy comparison to model predictions since atmospheric transport and dispersion models commonly produce time averaged concentrations at specific points. The system was designed primarily for SF6, but has been adapted to measure other gases such as carbon monoxide and Freon 12. (details)

The PIG's control system pumps air into Tedlar bags according to a programmed schedule.

Atmospheric Tracer Release Mechanisms FRD has designed, built, and operated tracer release systems for a wide variety of atmospheric tracer experiments. These have included systems for SF6, perfluorocarbons, and other materials and have covered a wide range of release rates. Each system is configured to meet the specific needs of the experiment it is designed for. We have built and operated vehicle, blimp, and aircraft-mounted release systems as well as the more common stationary systems. All release systems are computer-controlled with redundant release rate measurement and control. (details)

High rate mobile SF6 release mechanism used in the GAUNTLET project

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