Multiple level of CO2 fluxes over Beijing megacity with eddy covariance method

Based on the CO₂ fluxes measured with eddy covariance method from 2008 to 2012 at 47, 140 and 280m in Beijing 325m meteorological tower, we have investigated the exchange process of CO₂ flux between atmosphere and the urban surface in Beijing megacity. Because of the total vehicle control from 2011, the increasing rate of annual total CO₂ flux at 140m from 2008~2010 is 7.8% while from 2010~2012 is 2.3%. The average annual total CO₂ flux during the 5 year measurement is largest at 140m (6.41kg C m^-2 yr^-1) while at 47 (5.78 kg C m^-2 yr^-1) and 280m (3.99 kg C m^-2 yr^-1) are much smaller. The measured fluxes were highly dependent on the prevailing wind direction. The CO₂ fluxes at weekends are nearly the same as at weekdays because of the traffic restriction rule during Mon to Fri. Total vehicle numbers and population are main controlling factors of annual total CO₂ fluxes in Beijing. The CO₂ fluxes at three layers all present positive correlation with road fraction in the footprint area. The R-squares are respectively 0.69, 0.57 and 0.54 at 47, 140 and 280m. The decreasing fraction of vegetation will cause the increasing of annual total CO₂ flux and there is a exponential relationship between them. The annual total CO₂ flux is larger when the population density is higher.