[A-AS11] [JJ] 大気化学

[AAS11-P02] 波照間島および落石岬で観測された大気中N₂O濃度のトレンド、季節変動、および短期変動の解析

*遠嶋 康徳¹、勝又 啓一¹、町田 敏暢¹、石島 健太郎² (1.国立環境研究所、2.国立海洋研究開発機構)

キーワード：大気中N2O、温室効果ガス、季節変動、短期変動

Nitrous oxide (N₂O) is one of the important anthropogenic greenhouse gas in the atmosphere, having a GWP 265 times that of CO₂ for a 100-year timescale. To enhance understanding of the global N₂O cycle, the National Institute of Environmental Studies (NIES) has been carrying out in-situ observations of the atmospheric N₂O at Hateruma Island (HAT; lat. 24.1°N, long. 123.8°E) since March 1996 and at Cape Ochi-ishi (COI; lat. 43.2°N, long. 145.5°E) since June 1999 by using gas chromatographic systems. In this study, the trends, the seasonal variations, and the synoptic-scale variations of the atmospheric N₂O observed at both sites are examined. The N₂O concentrations at both sites steadily increased at an almost same rate of about 0.8 ppb/yr. Although the interannual variations in the growth rates seem to be rather small, relatively large increasing rates larger than 1.1 ppb/yr were observed for HAT in 1999-2000 and for HAT and COI in 2014-2015. The average seasonal cycles show the maxima in April for both sites and the minima in July for HAT and in September for COI. The peak-to-peak amplitudes of the average seasonal cycles are about 0.5 ppb and 0.8 ppb for HAT and COI, respectively. It should be noted that the seasonal amplitude for HAT seems to increase temporally at a rate of 0.012±0.007 ppb/yr (p=0.1) although that for COI doesn’t show a significant long-term change. In addition to the seasonal variations, synoptic scale variations are often observed especially at HAT during a period from November to March, when the polluted air masses are predominantly transported from the continental regions. The standard deviations of the detrended and deseasonalized time series of N₂O for the winter 5-month period for HAT show significant temporal increase. The EDGAR inventory estimation (v4.2, FT2012) shows that the anthropogenic N₂O emissions from China increase about 40% during 1996-2012. Therefore, the increasing trends in the amplitudes of the seasonal and short-term variations at HAT may reflect the anthropogenic emission increase in China.