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Isotope ratio infrared spectroscopy (IRIS) provides an in-situ technique for measuring δ13C in atmospheric CO2. A number of methods have been proposed for calibrating the IRIS measurements, but few studies have systematically evaluated their accuracy for atmospheric applications. In this study, we carried out laboratory and ambient measurements with two commercial IRIS analyzers and compared the accuracy of four calibration strategies. We found that calibration based on the 12C and 13C mixing ratios (Bowling et al., 2003) and that based on linear interpolation of the measured delta using the mixing ratio of the major isotopologue (Lee et al., 2005) yielded accuracy better than 0.06‰. Over a 7-day atmospheric measurement in Beijing, the two analyzers differed by 9.44±1.65‰ (mean ±1 standard deviation of hourly values) before calibration and agreed to within -0.02±0.18‰ after properly calibration. However, even after calibration the difference between the two analyzers showed a slight correlation with concentration, and this concentration dependence propagated through the Keeling analysis resulting in a much larger difference of 2.44‰ for the Keeling intercept. The high sensitivity of the Keeling analysis to the concentration dependence underscores the challenge of IRIS for atmospheric research. [ABSTRACT FROM AUTHOR]

Aims: To characterize the bacterial community dynamics over 1 year in two full-scale wastewater treatment systems operated under constant conditions and exhibiting stable performance. Methods and Results: Functional stability was defined and quantified by the effluent concentration of biological oxygen demand, total nitrogen and ammonia. Community dynamics were investigated using specific PCR followed by terminal restriction fragment length polymorphism (T-RFLP) of the 16S rRNA gene. The T-RFLP results indicated that during the period of functional stability, the bacterial community structures in two full-scale wastewater treatment systems were not stable, and the average change rates every 15 days of the two systems were 22·6 ± 6·9 and 21·6 ± 7·3%, respectively. The corresponding species with dominant T-RFs were determined by clonal sequencing and T-RFLP. Based on Pareto–Lorenz distribution curves, it was observed that only a small number of micro-organisms were numerically dominant in the two systems. Conclusions: The results of this study showed that, throughout the period of the study, the bacterial community structure changed significantly in two full-scale wastewater treatment systems despite the stable function. Significance and Impact of the Study: The findings enrich the theory involving the relation between bacterial community dynamics and functional stability in full-scale wastewater treatment plants. [ABSTRACT FROM AUTHOR]