Assessment of the biospheric contribution to surface atmospheric CO2 concentrations over East Asia with a regional chemical transport model

A regional chemical transport model, RAMS-CMAQ, was employed to assess the impacts of biosphere-atmosphere CO2 exchange on seasonal variations in atmospheric CO2 concentrations over East Asia. Simulated CO2 concentrations were compared with observations at 12 surface stations and the comparison showed they were generally in good agreement. Both observations and simulations suggested that surface CO2 over East Asia features a summertime trough due to biospheric absorption, while in some urban areas surface CO2 has a distinct summer peak, which could be attributed to the strong impact from anthropogenic emissions. Analysis of the model results indicated that biospheric fluxes and fossil-fuel emissions are comparably important in shaping spatial distributions of CO2 near the surface over East Asia. Biospheric flux plays an important role in the prevailing spatial pattern of CO2 enhancement and reduction on the synoptic scale due to the strong seasonality of biospheric CO2 flux. The elevation of CO2 levels by the biosphere during winter was found to be larger than 5 ppm in North China and Southeast China, and during summertime a significant depletion (≥7 ppm) occurred in most areas, except for the Indo-China Peninsula where positive bioflux values were found.