Increasing synoptic scale variability in atmospheric CO ₂ at Hateruma Island associated with increasing East-Asian emissions

In-situ observations of atmospheric CO ₂ and CH ₄ at Hateruma Island (24.05° N, 123.80° E, 47 m a.s.l), Japan shows large synoptic scale variations during a 6-month period from November to April, when the sampled air is predominantly of continental origin due to the Asian winter monsoon. Synoptic scale variations are extracted from the daily averaged values for the years between 1996 and 2007, along with the annual standard deviations (σ _CO2 and σ _CH4 for CO ₂ and CH ₄, respectively) for the relevant 6-month period. During this 6-month period the absolute mixing ratios of CO ₂ and CH ₄ at Hateruma are also elevated compared to those at two sites in the central North Pacific Ocean. The temporal change in σ _CO2 shows a systematic increase over the 12-year period, with elevated excursions in 1998 and 2003; there is no clear increase in σ _CH4. We also find that the σ _CO2/σ _CH4 ratio increases gradually from 1996 to 2002 and rapidly after 2002 without any extreme deviations that characterised σ _CO2. The σ _CO2/σ _CH4 ratio correlates closely with the recent rapid increase in fossil carbon emissions from China, as indicated in the Carbon Dioxide Information Analysis Center (CDIAC) database. This methodology can be applied to multiple chemical tracers of sufficient lifetime, for tracking overall changes in regional emissions.