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

Abstract. 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 ΔCH₄ / ΔCO₂, ΔCO / ΔCO₂, and ΔCO / ΔCH₄ 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 ΔCH₄ / ΔCO₂ and ΔCO / ΔCO₂ 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 ΔCH₄ / ΔCO₂ and ΔCO / ΔCO₂ show gradual decrease and increase, respectively, during the entire observation periods used in this study. The ΔCO / ΔCH₄ 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.