Determining diurnal fossil fuel CO2 and biological CO2 by Δ14CO2 observation on certain summer and winter days at Chinese background sites.

Diurnal atmospheric Δ14CO2 was measured on two consecutive days in summer and winter, 2016 at Shangdianzi, Lin'an and Luhuitou regional background sites, and at Waliguan global background site in China. The objectives of this study were to determine diurnal fossil fuel CO2 (CO2ff) and biological CO2 (CO2bio) concentrations and to ascertain the factors influencing them. Evident CO2ff inputs (0-33.0 ± 1.4 ppm) were found, with some small morning and afternoon rush hour signals. Particularly, the long-range transport of air masses influenced the seasonal differences and rapid diurnal variations in CO2ff. Diurnal CO2bio showed violent variations (-20.9-113.3 ppm), with high values at night and low or negative values during the daytime. Diurnal CO2bio variations resulted from the tradeoffs between photosynthetic CO2 uptake and biological respiration CO2 emission as well as atmospheric boundary layer heights variations. These results might help to understand the roles of fossil fuel sources and biological sources on atmospheric CO2 diurnal variations at Chinese background sites.