[Characteristics and Influencing Factors of Greenhouse Fluxes from Urban Lawn].

As an important component of urban green spaces, greenhouse gas uptake or emissions from urban lawns cannot be ignored. However, studies of greenhouse gas fluxes from subtropical urban lawns are relatively sparse. The static chamber-gas chromatography method was applied to monitor the ground-air exchange fluxes of various greenhouse gases(CO2, CH4, N2O, and CO) in typical urban lawns of Hangzhou City. Our results showed that the average fluxes had significant seasonal cycles but ambiguous diurnal variations. The grassland and the soil(naked soil without vegetation coverage) acted as sources of atmospheric N2O, with the average fluxes of (0.66±0.17) and (0.58±0.20) µg·(m2·min)-1 for N2O, respectively; however, they were also sinks of CH4 and CO, with the average fluxes of (-0.21±0.078) and (-0.26±0.10) µg·(m2·min)-1 for CH4 and (-6.36±1.28) and (-6.55±1.69) µg·(m2·min)-1 for CO, respectively. The average CO2emission fluxes of urban grassland and soil were(5.28±0.75) and (4.83±0.91) mg·(m2·min)-1, respectively. The correlation analysis indicated that the CO2 and N2O fluxes of grassland and soil were negatively correlated with precipitation, whereas the CH4 and CO fluxes were positively correlated with it. There was no significant correlation between grassland CH4 fluxes and soil temperature, and N2O fluxes had a significant negative correlation with soil temperature; the other greenhouse gas fluxes showed a significant positive correlation with soil temperature. In addition, the seasonal variation in CO2 (R2=0.371 and 0.314) and N2O(R2=0.371 and 0.284) fluxes from both grassland and soil was affected by precipitation, whereas CO fluxes (R2=0.290 and 0.234) were mainly driven by soil temperature compared with the other greenhouse gases.

[Monitoring of atmospheric CH4, CO, CO2, N2O and SF6 using three-channel gas chromatography].

China is approaching a critical period of carbon peak and carbon neutrality. To assess the impact of carbon peak and carbon neutrality measures, an accurate understanding of the variations of the spatial and temporal distribution of greenhouse gases is crucial. Gas chromatography, a classical approach for greenhouse gas observation, can be employed for the high-precision analysis of partial greenhouse gases. In this research, a new greenhouse gas analytical system capable of measuring five gases (CH4, CO, CO2, N2O and SF6) on a single instrument was developed based on the traditional gas chromatography approach. The following are the chromatographic operation conditions. The carrier gases were high purity N2(99.999%) and argon-methane (5% methane in argon, 99.9999%), and a stainless steel switching valve triggered the injection. Compressed CH4, CO, CO2, N2O and SF6 mixed standard gases were stored in a 0.029 m3 aluminum alloy steel cylinder for this experiment. After numerous rounds of calibration by Greenhouse Gas Laboratory of Atmospheric Sounding Center of China Meteorological Administration, the gas scale met the primary standard of World Meteorological Organization (WMO). The main performance of the system, including the measurement precision, accuracy and linear response, was tested. The results showed that the detection performance of the system met the quality standards of WMO/Global Atmospheric Watch (GAW). Precision test results indicated that the relative standard deviations (RSDs) of the mole fractions of CH4, CO, CO2, N2O and SF6 were 0.08%, 1.90%, 0.05%, 0.08%, and 0.66%, respectively. For the linear and accuracy test, the C1-C5 tested standard gases were employed and the deviations of five gases (CH4, CO, CO2, N2O and SF6) between the calculated mole fractions of the regression equation and calibrated mole fractions were 0.15×10-9, 0.20×10-9, 0.37×10-6, 0.35×10-9 and 0.02×10-12, respectively. For CH4, CO, CO2, N2O and SF6, the linear regression coefficients (R2) between the peak areas or heights and calibrated mole fractions were 0.9999. The linear regression residual and accuracy could roughly meet the expanded target of WMO/GAW quality control. The atmospheric greenhouse gases in the Hangzhou urban area were continuously measured from May 2021 to July 2021 using the developed system. The results revealed that atmospheric CH4, CO, CO2 and N2O have visible diurnal variation characteristics that were primarily affected by anthropogenic emissions. The target standard gases were measured every 2 h to monitor the stability of the system operation, and the gas mole fractions of the system response were routinely computed and compared with the assigned calibrated values. The results demonstrated that the system had good stability during the observation period and could meet the requirements of high-precision monitoring. The comprehensive test and trial operation results showed that the developed system had good precision, accuracy, linearity and stability.

Methane emission via sediment and water interface in the Bohai Sea, China.

Sediment is recognized as the largest reservoir and source of methane (CH4) in the ocean, especially in the shallow coastal areas. To date, few data of CH4 concentration in sediment have been reported in the China shelf seas. In this study, we measured CH4 concentration in sediment and overlying seawater columns, and conducted an incubation experiment in the Bohai Sea in May 2017. CH4 concentration was found to be ranged from 3.075 to 1.795 µmol/L in sediment, which was 2 to 3 orders of magnitude higher than that in overlying seawater columns. The surface sediment was an important source of CH4, while bottom seawater acted as its sink. Furthermore, the net emission rate via sediment water interface (SWI) was calculated as 2.45 µmol/(m2∙day) based on the incubation experiment at station 73, and the earthquake may enhance CH4 release from sediment to seawater column in the eastern Bohai Sea.