| The Shangdianzi and Lin’an stations are located at Jing-Jin-Ji and Yangtze economic regions, respectively. High precision observations of atmospheric CO2, stable carbon isotope(δ13C) and CO could help us understand the variation of their levels and estimate the carbon dioxide source/sink characteristics such as carbon isotopic signatures, which can provide the monitoring basic data and scientific technology support for understanding the mechanism of carbon cycle in China and making effective carbon emission reductive measurements. However, observation of δ13C in atmospheric CO2 is rarely reported in China so far. Based on the high precision δ13C analysis system, the study obtained several year data of δ13C from flask samples collected at SDZ and LAN. Combined with the data of CO2, we can estimate the carbon isotopic signature of carbon dioxide source/sink for SDZ and LAN. The data of CO2 and CO was also combined to obtain the CO2/CO emission ratio of combustion sources. In this study, we also evaluated the data interlaboratory compatibility and compared the isotopic effects on CO2 analysis systems. Moreover, simutaneous monitoring FTIR system of atmospheric CO2, δ13C(CO2) and CO is improved and evaluated for further field continuous observation.This study presents CO2 concentrations of air flask samples obtained at regional background stations SDZ and LAN in China from January 2007 to December 2013, as well as its stable isotope ratios(δ13C) during 2009 and 2013 at SDZ and during 2011 and 2013 at LAN, respectively. Non-polluted, mixed-well and representative background air samples are selected to represent background characteristics of atmospheric CO2 and δ13C over Jing-Jin-Ji and Yangzte River Delta regions. The concentrations of atmospheric CO2 observed at SDZ and LAN showed positive trend during the study period. Annual mean backgound CO2 levels obtained at SDZ varied from 385.6 ppm in 2007 to 398.1 ppm in 2013, higher than global baseline levels, and the averaged growth rate is 2.0 ppm yr-1. The averaged growth rate obtained at LAN is 2.7 ppm yr-1, and the annual mean backgound CO2 levels ranged from 388.3 ppm~405.8 ppm during 2007-2013, higher than SDZ, might owing to more energy consumption and carbon emissions observed at Yangtze River Delta regions than Jing-Jin-Ji areas. Atmospheric δ13C(CO2) levels obtained at SDZ and LAN present negative trends. The δ13C(CO2) values observed at SDZ decreased from-8.38‰ in 2009 to-8.52‰ in 2013, with a mean growth rate of-0.03‰ yr-1. The annual mean values of δ13C vary from-8.54‰ in 2011 to-8.75‰ in 2013 at LAN, with a growth rate of-0.080‰ yr-1, lower than SDZ(-0.042‰ yr-1) during the same periods. The absolute increase of CO2 from 2007 to 2008 reached the lowest level during 2007 and 2013, and the lowest level of monthly CO2 during July and September appeared in 2008, possibly due to relative less carbon emissions during 2008 Olympic Games period.Seasonal cycles of CO2 concentrations and δ13C(CO2) are observed to be obvious at SDZ and LAN. The maximum values of seasonal CO2 cycle appear in August, and the minimum levels appear in March at SDZ and January at LAN, respectively. The peak-to-peak amplitude of seasonal CO2 cycle is 23.9 ppm obtained at SDZ and 17.5 ppm at LAN. The monthly CO2 concentrations observed at LAN during 2007-2013 are higher than the MBL levels, which may indicate that Yangtze River economic region is a strong source within the same latitude zone. The monthly CO2 concentrations observed at SDZ in summer are lower than the MBL levels, which may indicate that Jing-Jin-Ji is a sink area within the same latitude zone.The sign of δ13C seasonal cycle is opposite to that of CO2, and the peak-to-peak amplitude is 1.03‰ at SDZ and 0.89‰ at LAN, respectively.The carbon isotopic signatures of CO2 sources/sinks(δs) were also discussed in this study. The averaged δs value for the whole year during 2009 and 2013 observed at SDZ(-22.86‰) is more positive than that obtained at WLG, indicating the variation of backgound CO2 may partly caused by C4 plants like corn. The δs value obtained at SDZ for heating season Ⅰ(Jan.01-Mar.14) is-21.30‰, while-25.39‰ for heating season Ⅱ(Nov.15-Dec.31), and for vegetative season(Mar.15-Nov.14) the δbio value was estimated to be-22.89‰, likely suggesting the significant impact of fossil fuel and corn straw combustions during winter heating season and biological activities during vegetative season. At LAN, the estimated δs values for heating season(December-February) is-23.27‰ and for vegetative season is-22.02‰(March-November) suggest the significant impact of fossil fuel combustions during winter heating season and biological activities during vegetative season. Moreover, atmospheric CO2 and CO data shows strong correlation during winter period observed at SDZ and LAN, the ΔCO2/ΔCO emission ratio obtained at SDZ and LAN is 36.9 ppm/ppm and 30.4 ppm/ppm, respectively, indicating the significant contribution from fossil fuel combustions.The analyzed data of atmospheric CO2、CO、δ13C(CO2) from flask samples obtained at Waliguan station was compared with NOAA, and the probability distribution of data difference conformed to Gauss fitting curve. The probability is 82.2% for ΔCO2 fall in the range of ±0.5 ppm, 78.7% for Δδ13C fall in the range of ±0.1‰, and 93.4% for ΔCO fall in the range of ±5 ppb. Non-dispersive infrared(NDIR) and cavity ring-down spectroscopy(CRDS) CO2 analyzers use 12CO2 isotopologue absorption lines and are insensitive to all, or in part, the other CO2-related isotopologues. This may produce biases in CO2 mole fraction measurements of a sample if its carbon isotopic composition deviates from that of the standard gases being used. The CO2 mole fractions error of natural atmospheric sample measured by Lo Flo and PICARRO G1301 using industial standards could reach 0.19 ppm and 0.2 ppm, respectively. According to the theoretical and experimental results, we concluded that the total CO2 mole fractions of samples with depleted isotopic compositions can be corrected based on their 12CO2 values calibrated by standard gases using Lo Flo and PICARRO G1301, if we know the δ13C and δ18O values.The real-time, automatic, highly accurate and efficient system for measuring the mixing ratios of CO2, δ13C(CO2), CO, CH4 and N2 O has been developed by combining the commercial FTIR system with an auto-sampling system and a working standard module. Using the working standard gases to calibrate the results of FTIR significantly improved the accuracy of the measurements. The standard deviation of atmospheric CO2, CH4, N2 O, CO and δ13C(CO2) measured by improved FTIR is 0.03 ppm、0.2 ppb、0.06 ppb、0.2 ppb、0.046‰, respectively, meeting the inter-laboratory compatibility requirements of WMO/GAW. During 6 days in-situ measurements of greenhouse gas outside our lab, the inaccuracy of target gas can reach 0.09 ppm、0.4 ppb、0.14 ppb、0.5 ppb、0.126‰ for CO2, CH4, N2 O, CO and δ13C(CO2), respectively. |
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