| Observations of atmospheric CO2 mole fraction and the 13C/12C ratio(expressed as ?13C)in urban airsheds provide constraints on the roles of anthropogenic and natural sources and sinks in local and regional carbon cycles.The high frequency in situ observation and calibration system we established has provided the possibility for long-term monitoring and investigation of the variation and its impact factors of hourly atmospheric CO2 and ?13C.(1)In this study,we report observations of these quantities in Nanjing at hourly intervals from March 2013 to August 2015,using a laser-based optical instrument.During experiment period,the mean CO2 mole fraction and ?13C were(439.7 ± 7.5)?mol mol-1 and(-8.48 ±0.56)‰ over this observational period.The peak monthly mean ?1C(-7.44‰?July 2013)was 0.74‰ higher than that observed at Mount Waliguan,a WMO(World Meteorological Organization)baseline site on the Tibetan Plateau and upwind of the YRD region.The temporal variation of ?13C in the atmosphere follows the seasonal variation of althropogenic and vegetation CO2 emission sources,showing a trend of winter depletion in summer.Among them,the ?13C value of the urbai atmosphere in Nanjing is significantly higher than that in the background atmosphere in summer,which is obviously different from the existing research.The highly ?13C-enriched signal was partly attributed to the influence of cement production in Nanjing.We hypothesized that the Miller-Tans method applied to the daytime and nighttime observations should yield the effective ?13C/12C ratio of surface sources at the regional(YRD)and the local(Nanjing)scale,respectively.According to the results of the Miller-Tans method,the effective source 13C/12C ratio in the YRD was-24.37‰,which was 0.21‰ higher than that in Nanjing.By combining inventory data on anthropogenic carbon sources and the atmospheric measurement of CO2 mole fraction and 13C/12C ratio in an isotopic partitioning framework,we inferred that natural ecosystems in the YRD were a negligibly small source of atmospheric CO2,with an average flux of(0.02 ± 0.22)mg m-2 s-1 for 2014.For comparison,the CarbonTracker inverse analysis reveals a small annual mean daytime biological flux(-0.01 mg m-2 s-1)for this region in 2014.(2)Beijing lauched similar observation as Nanjing from February 2013 to March 2014.By comparing the data of the two cities during the same period,the results show that the average atmospheric CO2 mole fraction in Nanjing was slightly higher than that of Beijing(0.6 ?mol mol-1),but the seasonal amplitude in Nanjing was smaller than in Beijing(Beijing:36.4 ?mol mol-1;Nanjing:30.0 ?mol mol-1).The results show that the urban atmospheric CO2 was controlled by the seasonal variation of the total anthropogenic CO2 emission and the emission intensity in local and regional areas.The energy consumption structure and its seasonal change are the two key factors which casued the differences between atmospheric ?13C value in these two cities and areas.The diurnal compositon of atmospheric CO2 and ?13C in Beijing showed different pattern of diurnal compositon with Nanjing.In Beijing,atmospheric CO2 appeared a sub-peak between 8:00 and 10:00 while ?13C showed a sub-trough at the same time.The CO2 emission from traffic jam was responsesible for this phenomemon.By using an isotopic partitioning framework,the CO2 emissions from natural gas combustion accounted for 7.8%to 16.0%of Beijing's winter total anthropogenic emissions in Beijing.(3)During the temperal control period(TC),was 21.0 ?mol mol-1 lower than that of the non-temporary control period(NC),and the ?13C value in TC was 0.29‰ higher than that in NC.The spatial distribution and probability of potential CO2 emission were also significantly different between TC and NC.CO and NO2 have a good correlation and homology with CO2 emissions,which can be further used as CO2 tracers for specific sources. |
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