High frequency CO2 and wind speed measurements were used to examine the urban
baseline eddy covariance CO2 flux and analyse the CO2 rich plume from a
local power station. A reliable relationship between high frequency CO2 maxima
and the rate of CO2 emission at the power station was established. This relationship
was shown to be highly dependant on wind speed. The ensemble mean
plume was found to be approximately Gaussian in horizontal profile with a width
dependant on wind speed. The relationship between peak CO2 mixing ratio and
averaging time was shown to be a simple power law with a time exponent of approximately
0.5. The large, short pulses in CO2 mixing ratio in the power plant
plume were found to have an approximately Lorentzian shape. These pulses generated
negative vertical eddy flux measurements so data from the plume sector
were necessarily excluded from the flux baseline results. The plume-excluded
flux had a similar magnitude and variability to those reported in other urban CO2
flux studies despite this site not being ideal due to the proximity of roughness
elements to the measurement point. A linear-eddy model was used to relate the
mean concentration plume profile to plume profiles for different percentiles of
concentration. It showed that for high concentration percentiles and short dispersion
times the plume width can be several times greater than the standard mean
concentration plume width.