Abstract. Emissions of greenhouse gases (GHGs) from the Indian subcontinent have increased during the last 20 years along with rapid economic growth; however, there remains a paucity of GHG measurements for policy-relevant research. In northern India and Bangladesh, agricultural activities are considered to play an important role in GHG concentrations in the atmosphere. We performed weekly air sampling at Nainital (NTL) in northern India and Comilla (CLA) in Bangladesh from 2006 and 2012, respectively. Air samples were analyzed for dry-air gas mole fractions of CO2, CH4, CO, H2, N2O, and SF6 and carbon and oxygen isotopic ratios of CO2 (δ13C-CO2 and δ18O-CO2). Regional characteristics of these components over the Indo-Gangetic Plain are discussed compared to data from other Indian sites and Mauna Loa, Hawaii (MLO), which is representative of marine background air. We found that the CO2 mole fraction at CLA had two seasonal minima in February–March and September, corresponding to crop cultivation activities that depend on regional climatic conditions. Although NTL had only one clear minimum in September, the carbon isotopic signature suggested that photosynthetic CO2 absorption by crops cultivated in each season contributes differently to lower CO2 mole fractions at both sites. The CH4 mole fraction of NTL and CLA in August–October showed high values (i.e., sometimes over 4000 ppb at CLA), mainly due to the influence of CH4 emissions from the paddy fields. High CH4 mole fractions sustained over months at CLA were a characteristic feature on the Indo-Gangetic Plain, which were affected by both the local emission and air mass transport. The CO mole fractions at NTL were also high and showed peaks in May and October, while CLA had much higher peaks in October–March due to the influence of human activities such as emissions from biomass burning and brick production. The N2O mole fractions at NTL and CLA increased in June–August and November–February, which coincided with the application of nitrogen fertilizer and the burning of biomass such as the harvest residues and dung for domestic cooking. Based on H2 seasonal variation at both sites, it appeared that the emissions in this region were related to biomass burning in addition to production from the reaction of OH and CH4. The SF6 mole fraction was similar to that at MLO, suggesting that there were few anthropogenic SF6 emission sources in the district. The variability of the CO2 growth rate at NTL was different from the variability in the CO2 growth rate at MLO, which is more closely linked to the El Niño–Southern Oscillation (ENSO). In addition, the growth rates of the CH4 and SF6 mole fractions at NTL showed an anticorrelation with those at MLO, indicating that the frequency of southerly air masses strongly influenced these mole fractions. These findings showed that rather large regional climatic conditions considerably controlled interannual variations in GHGs, δ13C-CO2, and δ18O-CO2 through changes in precipitation and air mass.
We developed a battery-powered carbon dioxide (CO 2 ) measurement system for monitoring at the summit of Mt. Fuji (3776 m a.s.l.), which experiences very low temperatures (below −20 • C) and severe environmental conditions without access to gridded electricity for 10 months (from September to June). Our measurement system used 100 batteries to run the measurement unit during these months. These batteries were charged during the 2-month summer season when gridded electricity was available, using a specially designed automatic battery-charging system. We installed this system in summer 2009 at the Mt. Fuji weather station; observations of atmospheric CO 2 concentration were taken through December 2015. Measurements were never interrupted by a lack of battery power except for two cases in which lightning damaged a control board. Thus we obtained CO 2 data during about 94 % of the 6-year period. Analytical performances (stability and accuracy) were better than 0.1 ppm, as tested by checking working standards and comparisons with flask sampling.Observational results showed that CO 2 mole fractions at Mt. Fuji demonstrated clear seasonal variation. The trend and the variability of the CO 2 growth rate observed at Mt. Fuji were very similar to those of the Mauna Loa Observatory (MLO). Seasonally, the concentration at Mt. Fuji was 2-10 ppm lower in summer and 2-12 ppm higher in winter than those at MLO. The lower concentrations at Mt. Fuji in summer are mainly attributed to episodes of air mass transport from Siberia or China, where CO 2 is taken up by the terrestrial biosphere. On the other hand, the relatively higher concentrations in winter seem to reflect the high percentage of air masses originating from China or Southeast Asia dur-ing this period, which carry increased anthropogenic carbon dioxide. These results show that Mt. Fuji is not very influenced by local sources but rather by the sources and sinks over a very large region.Thus we conclude that, as this system could provide stable measurement data with relatively easy operation for 6 years at Mt. Fuji, it could be a useful monitoring technique for remote background sites elsewhere.
Evaluation of carbon dioxide (CO 2) sinks in forest areas of East and Southeast Asia (especially tropical regions) is important for assessing CO 2 budgets at the regional scale. To evaluate the CO 2 flux of large forest areas, we collected vertical CO 2 profiles over the forest using a CO 2 sonde and measured surface CO 2 concentrations around the forest using continuous CO 2 measurement equipment. These observations were performed over a typical northern forest (Hokkaido) in Japan, a subtropical forest island (Iriomote Island) in Japan, and a tropical forest in Borneo Island. We detected the differences in CO 2 vertical profiles between dawn and daytime, and at the upwind and downwind sites of the forests with the observational results from the CO 2 sonde. We also clarified that CO 2 concentrations during daytime at the downwind sites (affected by the forest) were systematically lower than those at the upwind sites (not affected by the forest). In contrast, CO 2 concentrations during dawn at the downwind sites were larger than those at the upwind site. We estimated the CO 2 fluxes (μmol m −2 s −1) at dawn and daytime of the forests from these observational results. The CO 2 fluxes of Borneo's forest were very large (16.5 and −37.7 at dawn and daytime, respectively), whereas the CO 2 fluxes of the forests in Hokkaido and Iriomote were lower (3.9 to 11.8 at dawn and −11.8 to −15.0 at daytime). These evaluated values were consistent with fluxes measured by the eddy-covariance method in the same region. Thus, use of the CO 2 sonde to collect observations of CO 2 vertical profiles was considered to be an effective method to verify CO 2 absorption and emission in large forest areas. This method can also be used to evaluate dynamic CO 2 absorption and emission processes in tropical forests.
Abstract. We developed a battery-operated carbon dioxide (CO2) measurement system and successfully observed atmospheric CO2 concentrations at the summit of Mt. Fuji (3776 m a.s.l.) in Japan throughout the year since 2009, in spite of no power supply and severe low temperature over 10 months of a year. The observational results from 2009 to 2015 showed that CO2 concentration at Mt. Fuji in summer and in winter was about 2–10 ppm lower and 2–12 ppm higher than at the Mauna Loa observatory (MLO), respectively. These episodic low concentrations at Mt. Fuji in summer have been cited as evidence that air masses originate from Siberia or China, which are affected by terrestrial CO2 uptakes. The relatively higher concentrations in winter were observed by air masses originated from China or Southeast Asia. The difference in monthly average CO2 concentration between Mt. Fuji and MLO appeared to increase from 2009 to 2015. Interannual variability and growth rate of CO2 concentration were similar both at Mt. Fuji and MLO, 13 ppm increase from 2009 to 2015, but the annual average concentration at Mt. Fuji was about 1 ppm higher than at MLO. Monthly averaged CO2 concentration at Mt. Fuji exceeded 400 ppm in April 2013. Recent CO2 concentration in 2015 at Mt. Fuji was about 62 ppm higher than the previous record measured in 1980. To evaluate a regional representative of our measurement data, CO2 values observed at Mt. Fuji were compared with airborne observations. They showed very good agreement with each other, indicating that Mt. Fuji was a representative site at which to monitor CO2 concentration in the mid-latitude Asian region.
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