WAVELET ANALYSIS OF CARBON DIOXIDE FLUXES IN THE SURFACE LAYER ABOVE A DENSELY BUILT CITY CENTRE AT NIGHT

摘要

Significant bursts in CO_2 concentration are seen throughout nocturnal time series at a densely built site in Marseille. They are most pronounced during the late evening hours when there is strong correlation between the atmospheric structures observed in the temperature and CO_2 time series at turbulent scales. Evidence suggests that these bursts, observed above roof-level, are related to intermittent venting of sensible heat from the warmer urban canopy layer. However, later in the night, the reduced gradient in CO_2 concentrations with height, perhaps due to local advection in the UBL and/or reduced traffic emissions in the UCL, limits the value of CO_2 as a tracer of convective plumes in the UBL.