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

摘要

In situ observation of the atmospheric CO_2, CH_4, and CO mixing ratios at Hateruma Island (HAT, 24.05oN, 123.80oE) 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 ?CH_4 /?CO_2, ?CO/?CO_2, and?CO/?CH_4 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 ?CH_4 /?CO_2 and ?CO/?CO_2 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 ?CH_4 /?CO_2 and ?CO/?CO_2 show gradual decrease and increase, respectively, during the entire observation periods used in this study. The ?CO/?CH_4 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 CH_4 and CO emissions from China under the assumption that the estimate of the fossil-fuel-derived CO_2 emissions based on the energy statistics are accurate. The estimated annual CH_4 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.