Assessment of spatio-temporal distribution of CO2 over greater Asia using the WRF-CO2 model

In-depth knowledge of global and regional carbon budget is required for effective policymaking to mitigate the global climate change. However, Asian carbon budget shows large uncertainty due to both lack of sufficient observations and detailed understanding of the existing CO2 observations. A regional air quality model (WRF-CO2) is set up for simulating atmospheric CO2 variations over the greater Asia region (68-124 degrees E, 2 degrees S-45 degrees N) for the period 2010-2012. The WRF-CO2 simulations are compared with observations from nine sites and a global Atmospheric Chemistry Transport Model (ACTM). The comparisons suggest WRF-CO2 simulation is able to capture large scale features in the observed variabilities, with varied ability at fine scales depending on representation of surface fluxes and meteorology around the observation sites. Analysis of CO2 signals from individual flux components suggests that ocean flux has least contribution to the CO2 variation (<10%). Four sites (Mt. Waliguan, Nainital, Cape Rama and Lulin) show dominance of biospheric flux over fossil flux to the CO2 variation (>80%). CO2 mixing ratios are found to be maximum in northern hemisphere (NH) winter over East Asia, while they are maximum in NH spring over Indian subcontinent. Observed peak-to-trough seasonal amplitude is lowest (4.5 ppm) for the site Bukit Koto Tabang, Indonesia and highest (29.5 ppm) for Shangdianzi in China. Statistical analysis from monthly mean CO2 time series shows that correlation coefficient and normalised standard deviation with observations, are generally equal or better for the WRF-CO2 than the coarser resolution ACTM. Study of synoptic scale CO2 variations shows that the WRF-CO2 is able to better resolve daytime signatures than those in the night. Year-to-year CO2 variations of seasonal cycle amplitude is highest (similar to 5 ppm) at Nainital, India compared to all other sites.