Characteristics of CO₂ Concentration and Flux in the Beijing Urban Area

Since February 2012, CO 2 , H 2 O, and wind data at 10 Hz have been measured by the open‐path eddy covariance systems at 8, 16, 47, 80, 140, 200, and 280 m above ground level on the 325 m Beijing meteorological tower. Analysis of the data from 2013 to 2016 indicates that the annual averaged CO 2 concentration increased and the local and regional CO 2 emission decreased with the sequestration of background CO 2 concentration. The maximum values occurred during winter, and the minimum values occurred during summer. During spring, summer, and autumn, there was a constant CO 2 flux layer from 47 m to 140 m. However, during winter, CO 2 flux increased with height, and the maximum appeared at approximately 140 m and then decreased with height. Above 47 m, the CO 2 fluxes were represented as the net efflux, and below 16 m, the fluxes were near zero or a net uptake. At all observed heights, the diurnal variation in the CO 2 concentration displayed a clear cycle with a peak corresponding to the morning transportation rush hour. The local wavelet power spectra of the CO 2 concentration, CO 2 flux, and other meteorological elements identified significant cross‐wavelet powers near the 24 h and 365 day bands for the CO 2 concentration and flux with temperature, wind speed, friction velocity, and turbulent kinetic energy.