Tracer Technology Group
Local Projects
PFTs have been widely used to provide data for model verification and
refinement on the scale of a few to tens of miles. Two major
experiments in which BNL applied PFT tracer technology are the Vertical
transport and mixing (VTMX) experiment held in Salt Lake City in 2000 and
the Urban Dispersion Program being conducted from 2004 - 2007.
A meteorological field measurement program was conducted in the Salt Lake
Valley during October 2000. Scientists from government laboratories,
universities, and private industry carried out studies of the processes
contributing to the vertical transport and mixing of momentum, heat, and
water vapor in the lowest few thousand feet of the atmosphere. Such
processes affect how wind speed, temperature, and moisture vary with height
and how atmospheric pollutants may be distributed over an area. Vertical
transport and mixing (VTMX) processes play a significant but not yet
well-defined role in the transport, dilution, and subsequent fate of
pollutants in urban basins located within intermountain basin regions.
In the VTMX program, the important role of tracers in following the effects
of these processes has been recognized and the perfluorocarbon tracer (PFT)
technology was used in this four-year program (more...). The
results of this work program increased the fundamental understanding of
these phenomena, which may eventually lead to improved air quality and
weather forecasting models (more...).
The New York City Urban Dispersion Program is a four-year (2004-2007)
multi-National Laboratory,
multi-Federal Agency research project whose major objective is to study how air
flows in a city
environment. The deep canyons created by the tall buildings in New York create
challenges in
predicting air flow. Field studies using perfluorocarbon gas tracers have been
and will be performed to provide
data that can help improve and validate computer models that simulate the
atmospheric movement of
contaminants within cities, and around, into and building interiors and subways
(more...).
Ameriflux
Tower Footprint Studies
There is a natural cycle in which CO2
moves between the atmosphere and the ocean and the atmosphere and the
terrestrial biosphere.
Understanding the dynamics of the carbon cycle is essential to predicting
future atmospheric CO2 levels.
Eddy covariance methods are used at AmeriFlux sites to measure the
net ecosystem exchange (NEE) as measured by the flux of CO2, H2O
and other fluxes. These
techniques have limitations.
Generalization of tower flux results requires a detailed knowledge of the
degree to which the area responsible for the flux of CO2 and
other gases at the measurement site (the footprint) represents the regional
biosphere. There are also other
problems with eddy correlation methods that occur during periods of strong
atmospheric stability, particularly during calm nocturnal periods. PFT
Studies are being conducted in Florida and the Savannah River Site to
resolve some of these issues.
Florida
The Florida Footprint experiments were a
series of field programs in which perfluorocarbon tracers were released in
different configurations centered around a flux tower.
The concentrations of these tracers were measured at different levels
on the tower. These data will be
compared to the meteorological and CO2 flux data to determine
relationships between the tower footprint, the measured fluxes and the
meteorological conditions and will be used to improve and validate models
used to predict tower footprints.
Details can be found at (more...)
Savannah River
Super Site Studies
There have been a limited number of
experiments designed to validate footprint models, and address the
applicability of applying current models and the problems with using them in
non-ideal conditions. Previous
tracer experiments to validate footprint models have been conducted using a
single tracer, SF6 and have not been preformed under stable
nocturnal conditions.
The nocturnal boundary layer technique
(NBL) has been presented as a possible alternative to the eddy covariance
technique for the determination of CO2 and other fluxes in stable
nighttime conditions. This
technique is based on the assumption that the nocturnal boundary layer is
isolated from the upper levels of the atmosphere and the effects of surface
sources and sinks are trapped in this relatively shallow layer.
In the summer of 2007 we will conduct a
series of annual Perfluorocarbon Tracer (PFT) experiments at the Integrated
Carbon Flux Super-site. These
programs are funded by the Department of Energy Terrestrial Carbon program.
The goals of the PFT experiments will be to test the NBL method under
a variety of meteorological conditions, determine the effects of the Low
Level Jet (LLJ) on surface fluxes and their measurement, map the tower flux
footprint under different atmospheric conditions and examine the effects on
CO2 measurements at the tower, and quantify the effects of
inhomogenities in the flux source region, and examine effects of non-local
forcing on fluxes at the tower.
The tracer concentration data will be used
to empirically determine the tower footprint.
The data will be compared with models prediction of footprints.
These data will be compared to the meteorological and CO2
flux data to determine relationships between the tower footprint, the
measured fluxes and the meteorological conditions.
Measured background PFT levels will be compared with those observed
at other locations in the
US
and at other sites around the globe.
The results of the first field program
will be used to refine the design of the second program, to expand the scope
or focus on interesting findings that require further resolution. The PFT
tests will be coordinated with the other researchers at the Super Carbon
Flux site to optimize the utility of all resources.
Last Modified: November 12, 2009
Please forward all questions about this site to:
Linda Satalino
|
