RADON-222 AS AN AIRMASS TRACER
Principal Investigator:
Thomas P. Carsey
Objective:
Application of Radon-222 measurements for air mass characterization in support of
atmospheric chemistry programs.
Rationale: Within the planetary boundary layer, ozone and its precursors can be removed quickly by surface
deposition. Additionally, the catalyzing effect of NOx for ozone production is more efficient in
the cleaner air above the PBL. For the long-range transport of these trace gases, the exchange
between the PBL and the free troposphere is thus a critical parameter. Due to its ground source,
Rn-222 can be used to constrain the exchange between the PBL and the free troposphere. As a
chemically inert gas, Rn-222 has a well known sink term (radioactive decay with a half-life of 3.8
days and a reasonably well defined source (emissions from soils, no upper air source)).
Simultaneous Rn-222 measurements can provide an independent constraint for interpretation of
measurements of chemically active species. For example, measurable Rn-222 concentrations in an
air mass with high ozone concentrations are a clear indication of the presence of boundary layer
air, rather than a stratospheric source of the encountered ozone.
Method:
Samples are collected with an aircraft sampler developed by the PI. For a
typical sample radon from 50 liters of air is extracted on activated
charcoal (at ambient temperature).
Currently 24 samples can be collected during one research flight. Radon is then extracted in the
laboratory and transferred into ionization chambers (measurement capacity is 8 samples per 12
hours and is currently being doubled).
Accomplishment:
The radon aircraft sampler was first used during the
NARE Summer Intensive in 1993. A total of
68 samples was collected during 9 flights over the North Atlantic Ocean and over the continent in
the vicinity of Nova Scotia and New Brunswick, Canada. These results are described in detail in a
paper recently submitted to JGR.
An improved version of the aircraft sampler and measurement system was deployed in summer
1995 during the Southern Oxidant Study (SOS), a multi-agency project under the supervision of
the Tennesse Valley Authority at Nashville, TN. The effort was integrated into the measurement
program organized by NOAA's Aeronomy Laboratory (Boulder, CO). The sampler was installed
on the NOAA P-3 aircraft and about 160 samples were collected and measured. This data set is
currently being evaluated.
This instrument is currently being rebuilt. The present system is shown here.
Key reference:
Zaucker, F. , Daum, P., Wetterauer, U., Berkowitz, C., Kromer, B., and Broecker, W. S.,
Atmospheric Radon-222 Measurements During the 1993 NARE Intensive, submitted to JGR,
1995.
Xing, L., Zaucker, F., Trainer, M., McKeen, S. A., and Liu, S. C., Rn-222 Simulations as a Test
of a 3-D Regional Transport Model, submitted to JGR, 1995.
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