Temporal changes in the emissions of CH4 and CO from China estimated from CH4/CO2 and CO/CO2 correlations observed at Hateruma Island

In situ observation of the atmospheric CO2, CH4, and CO mixing ratios at Hateruma Island (HAT, 24.05 degrees N, 123.80 degrees E) often show synoptic-scale variations with correlative elevations during winter, associated with air transport from the East Asian countries. We examine winter (November-March) trends in Delta CH4 / Delta CO2, Delta CO/ Delta CO2, and Delta CO/ Delta CH4 observed at Hateruma over the period 1999 to 2010. To investigate the relationship between the East Asian emissions and the short-term variations in the atmospheric mixing ratios, we use the FLEXPART Lagrangian particle dispersion model (LPDM). The observed ratios Delta CH4 / Delta CO2 and Delta CO/ Delta CO2 both show an overall gradual decrease over the study period due to a recent rapid increase in fossil fuel consumption in China. We note, however, that the decreasing rates of Delta CH4 / Delta CO2 and Delta CO/ Delta CO2 show gradual decrease and increase, respectively, during the entire observation periods used in this study. The Delta CO/ Delta CH4 slope, on the other hand, shows an increasing trend during 1999-2004 but a decrease during 2005-2010. Calculation of the concentration footprint for the atmospheric observation at HAT by using the FLEXPART LPDM indicates that most of the short-term variations are caused by emission variations from northern and eastern China. Combined with a set of reported emission maps, we have estimated the temporal changes in the annual CH4 and CO emissions from China under the assumption that the estimate of the fossil-fuel-derived CO2 emissions based on the energy statistics are accurate. The estimated annual CH4 emissions, corresponding to nonseasonal sources or anthropogenic sources without rice fields, show a nearly constant value of 39 +/- 7 TgCH(4) yr(-1) during 1998-2002, and then gradually increase to 46 +/- 8 TgCH(4) yr(-1) in 2009/2010. The estimated annual CO emissions increase from 134 +/- 32 TgCO yr(-1) in 1998/1999 to 182 +/- 42 TgCO yr(-1) in 2004/2005, level off after 2005, and then slightly decrease to less than 160 TgCO yr(-1) in 2008-2010.