• Continuous measurement of atmospheric CO 2 and δ 13 C in Beijing. • δ 13 C depleted in heating season and enriched in vegetative season.• Diurnal variation of δ 13 C showed two peaks in heating season.• Coal combustion was the main local CO 2 source. • δ 13 C showed significant liner relationship with air quality index (AQI). G R A P H I C A L A B S T R A C Ta b s t r a c t a r t i c l e i n f o The stable isotope composition of atmospheric CO 2 can be used as a tracer in the study of urban carbon cycles, which are affected by anthropogenic and biogenic CO 2 components. Continuous measurements of the mixing ratio and δ 13 C of atmospheric CO 2 were conducted in Beijing from Nov. 15, 2012 to Mar. 8, 2014 including two heating seasons and a vegetative season. Both δ 13 C and the isotopic composition of source CO 2 (δ 13 C S ) were depleted in the heating seasons and enriched in the vegetative season. The diurnal variations in the CO 2 mixing ratio and δ 13 C contained two peaks in the heating season, which are due to the effects of morning rush hour traffic. Seasonal and diurnal patterns of the CO 2 mixing ratio and δ 13 C were affected by anthropogenic emissions and biogenic activity. Assuming that the primary CO 2 sources at night (22:00-04:00) were coal and natural gas combustion during heating seasons I and II, an isotopic mass balance analysis indicated that coal combustion had average contributions of 83.83 ± 14.11% and 86.84 ± 12.27% and that natural gas had average contributions of 16.17 ± 14.11% and 13.16 ± 12.27%, respectively. The δ 13 C of background CO 2 in air was the main error source in the isotopic mass balance model. Both the mixing ratio and δ 13 C of atmospheric CO 2 had significant linear relationships with the air quality index (AQI) and can be used to indicate local air pollution conditions. Energy structure optimization, for example, reducing coal consumption, will improve the local air conditions in Beijing.

Abstract. Isotope ratio infrared spectroscopy (IRIS) permits continuous in situ measurement of CO 2 isotopic composition under ambient conditions. Previous studies have mainly focused on single IRIS instrument performance; few studies have considered the comparability among different IRIS instruments. In this study, we carried out laboratory and ambient measurements using two Picarro CO 2 δ 13 C analyzers (G1101-i and G2201-i (newer version)) and evaluated their performance and comparability. The best precision was 0.08-0.15 ‰ for G1101-i and 0.01-0.04 ‰ for G2201-i. The dependence of δ 13 C on CO 2 concentration was 0.46 ‰ per 100 ppm and 0.09 ‰ per 100 ppm, the instrument drift ranged from 0.92-1.09 ‰ and 0.19-0.37 ‰, and the sensitivity of δ 13 C to the water vapor mixing ratio was 1.01 ‰ / % H 2 O and 0.09 ‰ / % H 2 O for G1101-i and G2201-i, respectively. The accuracy after correction by the two-point mixing ratio gain and offset calibration method ranged from −0.04-0.09 ‰ for G1101-i and −0.13-0.03 ‰ for G2201-i. The sensitivity of δ 13 C to the water vapor mixing ratio improved from 1.01 ‰ / % H 2

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Abstract:Transition from forest to rubber (Hevea brasiliensis Muell. Arg.) plantation has occurred in tropical China for decades. Rubber has been planted on 1 million ha to provide raw materials to the rubber industry. The role of various-aged rubber plantations in carbon (C) sequestration remains unclear. The biomass C accumulation including latex C and C distribution in soil of five different-aged stands (7,13,19,25 and 47 years old) were examined. The total biomass C stock (TBC) and total net primary productivity (NPP total ), whether with or without latex C, had a close quadratic relationship with stand age. Regardless of stand age, around 68% of the C was stored in aboveground biomass, and NPP latex contributed to approximately 18% of C sequestration. Soil organic carbon stock in the 100-cm depth remained relatively stable, but it lost about 16.8 Mg ha −1 with stand age. The total ecosystem C stock (TEC) across stands averaged 159.6, 174.4, 229.6, 238.1 and 291.9 Mg ha −1 , respectively, of which more than 45% was stored in the soil. However, biomass would become the major C sink rather than soil over a maximal rubber life expectancy. Regression analysis showed that TEC for rubber plantation at 22 years is comparable to a baseline of 230.4 Mg ha −1 for tropical forest in China, and would reach the maximum value at around 54 years. Therefore, rubber plantation can be considered as alternative land use without affecting net forest ecosystem C storage. In addition to the potential C gains, a full set of ecosystem and economic properties have to be quantified in order to assess the trade-offs associated with forest-to-rubber transition.

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Abstract. The isotope ratio infrared spectroscopy (IRIS) permits in situ and continuous measurements of CO2 isotopic composition under ambient conditions. Previous studies mainly focused on single IRIS instrument performance, few studies have paid attention to the comparability among different IRIS instruments. In this study, we carried out laboratory and ambient measurements of two Picarro CO2 δ13C analyzers (G1101-i and G2201-i), and evaluated their performance and comparability. The best precision were 0.08 ~ 0.15 ‰ and 0.01 ~ 0.04 ‰, the dependence of δ13C on CO2 concentration were 0.46 ‰ per 100 ppm and 0.09 ‰ per 100 ppm, the instrument drift ranged from 0.92 ~ 1.09 ‰ and 0.19 ~ 0.37 ‰. After upgradation of G1101-i, the sensitivity of δ13C on water vapor mixing ratio were 0.15 ‰ / % H2O and 0.13 ‰ / % H2O for the G1101-i and G2201-i, respectively. The accuracy after corrected by the two-point mixing ratio gain and offset calibration method ranged from −0.04 ~ 0.09 ‰ and −0.13 ~ 0.03 ‰ for G1101-i and G2201-i, respectively. Atmospheric δ13C measurements captured the rapidly changing atmospheric δ13C signals, with the difference of 0.07 ± 0.24 ‰ and 0.05 ± 0.30 ‰ between G1101-i upgraded before and after and G2201-i. Before upgradation of G1101-i, a significant linear correlation was observed between the δ13C difference and water vapor concentration, but there is no significant correlation after upgradation of G1101-i. The difference of Keeling intercept values between G1101-i and G2201-i decrease from 1.24 ‰ to 0.36 ‰, which indicate the importance of consistency among different IRIS instruments.

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