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The Measurements of Anthropogenic Gases and Natural Emissions from Tall Towers (MAGNETT) program of NOAA/CMDL utilizes existing tall (>400 m) towers as sampling platforms for in-situ and flask sample analyses of atmospheric trace gases. The program began in June, 1992, with continuous monitoring of CO2 and 222Rn mixing ratios, wind speed and direction, temperature, and relative humidity at three levels up to 500 m on the WITN TV transmitter tower in eastern North Carolina. Weekly flask sampling at WITN was started in July, 1992, with filled flasks returned to the Boulder laboratory for the analysis of CH4, CO, H2, CO2, and 13C/12C and 18O/16O isotope ratios in CO2.
The data from WITN show diurnal cycles in CO2 mixing ratios at the 50, 120 and 500 m measurement levels, with more pronounced cycles near the ground. The diurnal cycles are modulated by surface uptake and release of CO2 by vegetation and soils, emissions from fossil fuel combustion, and by the diurnal development of the planetary boundary layer. The contribution of regional fossil fuel combustion sources is especially evident in winter, when biological fluxes are small. In October, 1994, an automated 4-channel gas chromatograph (GC) was installed at WITN to measure combustion products (CO, CH4, H2) and other anthropogenic trace gases (CFCs, methyl chloroform, carbon tetrachloride, chloroform, sulfur hexafluoride, perchloroethylene) concurrently with CO2.
The WLEF TV transmitter tower in northern Wisconsin became the second site for the MAGNETT program in October, 1994. Mixing ratios of CO2 are continuously monitored at six different levels up to 400 m, and wind speed, wind direction, temperature and relative humidity are measured at three levels. A weekly flask sampling program is also active at LEF. In the near future, an automated 2-channel GC will be installed at this site to measure CO, CH4, H2, CFCs, methyl chloroform and carbon tetrachloride.
Monitor CO2 and other radiatively important trace gases over the continental interior for comparison with "background" (e.g., marine boundary layer, mountain top) sites, to deduce continental sources and sinks.
Determine mean mixing ratios of trace gases in the planetary boundary layer, and diurnal cycles as a function of height. The data will also be useful for testing planetary boundary layer parameterizations in regional and global circulation models.
Characterize and monitor regional emission signatures of
To simultaneously measure many species (halocarbons, CO) which will help determine the relative influence of biogenic processes vs. fossil fuel combustion on CO2 mixing ratios, and the relative influence of biogenic vs. anthropogenic CH4 emissions.
Determine vertical gradients of radiatively important trace gases over the continent to estimate surface sources/sinks.
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