Temporal changes in the emissions of CH 4 and CO from China estimated from CH 4 / CO 2 and CO / CO 2 correlations observed at Hateruma Island

In situ observation of the atmospheric CO2, CH4, and CO mixing ratios at Hateruma Island (HAT, 24.05 N, 123.80 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 1CH4 /1CO2, 1CO /1CO2, and1CO /1CH4 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 1CH4 /1CO2 and 1CO /1CO2 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 1CH4 /1CO2 and 1CO /1CO2 show gradual decrease and increase, respectively, during the entire observation periods used in this study. The 1CO /1CH4 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 TgCH4 yr−1 during 1998–2002, and then gradually increase to 46± 8 TgCH4 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.