Characteristics of CO2 Concentration and Flux in the Beijing Urban Area

Since February 2012, CO2, H2O, and wind data at 10Hz have been measured by the open-path eddy covariance systems at 8, 16, 47, 80, 140, 200, and 280m above ground level on the 325m Beijing meteorological tower. Analysis of the data from 2013 to 2016 indicates that the annual averaged CO2 concentration increased and the local and regional CO2 emission decreased with the sequestration of background CO2 concentration. The maximum values occurred during winter, and the minimum values occurred during summer. During spring, summer, and autumn, there was a constant CO2 flux layer from 47m to 140m. However, during winter, CO2 flux increased with height, and the maximum appeared at approximately 140m and then decreased with height. Above 47m, the CO2 fluxes were represented as the net efflux, and below 16m, the fluxes were near zero or a net uptake. At all observed heights, the diurnal variation in the CO2 concentration displayed a clear cycle with a peak corresponding to the morning transportation rush hour. The local wavelet power spectra of the CO2 concentration, CO2 flux, and other meteorological elements identified significant cross-wavelet powers near the 24h and 365day bands for the CO2 concentration and flux with temperature, wind speed, friction velocity, and turbulent kinetic energy.