Monitoring And Analysis Of Background Concentrations Of Carbon Dioxide And Methane At Zhongshan Station, Antarctica

Global atmospheric concentrations of main greenhouse gases are accelerating in recent years, global warming is closely related to human life, causing worldwide attention. The Antarctic continent which is far away from human settlements, is an ideal region to monitor background concentrations of greenhouse gases with little environmental pollution, it can be considered as background of the global atmosphere. With the support of the 4th International Polar Year (2008/2009) China Action Plan, continuous CO2 monitoring was instituted at Zhongshan Station with advanced measuring instruments. In this paper, an analysis of CO2 and CH4 concentrations, measured continuously from 2010 through 2013, along associated with Flask Bottle sampling data and surface meteorological observations and NCAR/NCEP data at Zhongshan Station, are presented and discussed. After screening and culling abnormal values, we try to carry on a preliminary discussion and analysis of diurnal variation, daily variation and seasonal variation and the annual change of background characteristics of CO2 and CH4, at the same time compare the data at Zhongshan Station with other stations. Some preliminary results are as follows:Meteorological data shows that the prevailing winds are persistent easterly winds with 83.1%, coming from the quadrant in the ENE, E and ESE.94.7% of winds fall in the 0.5 m·s-1 to 15 m·s-1 range with only 1% of winds above 20 m·s-1.The concentrations of CO2 observed at Zhongshan Station is only slightly affected by wind direction and speed. Local pollution from the station under westerly and calm winds accounted for only 1.7% of the total measurement period. Both throughout the year and each season, the distribution of concentrations of CH4 is uniform under different wind direction and wind speed scale, local pollution may account for only 1% of the total measurement period. Once this contamination is removed from the data set, the observations can be used to represent the background concentrations of CO2 and CH4 measured on the east coast of the Antarctic continent.The average daily range of CO2 and CH4 mole fraction in all four seasons are small. The results, therefore, suggest that there are no strong CO2 and CH4 sources and diurnal changes in the characteristics of the CO2 sinks upwind of the station. This also indicates that the observation point on the east coast of Antarctica on a rocky outcropping without vegetation in summer and covered by snow in the other three seasons does not have a regional influence on the observations of background CO2 and CH4.The average monthly mole fraction changes exhibit a seasonal pattern as well as a steady increase in background CO2 mole fractions, the seasonal variation of CO2 mole fractions at Zhongshan reaches a minimum in March with a peak in November. As such, from Austral autumn through winter into spring (March-November), the cycle period for CO2 mole fractions is largest while the CO2 cycle in spring is noticeably slower than that in autumn and winter. Summer (December-March) is the period when the mole fractions are the lowest. The monthly mean CO2 mole fraction measured at Zhongshan station is similar to that of other stations in Antarctica, and their annual amplitudes are all within the range of 384-392 ppm during the period 2010-2013. The annual increase in recent years is about 1.5-2.2 ppm.Flask Bottle sampling data of CH4 was in good agreement with On-line data. The average monthly mole fraction changes is quite smooth from 2010 through 2013, the monthly amplitudes are all within the range of 1722-1784 ppb with obvious seasonal variation and interannual variability, present a steady growth trend. The seasonal variation of CH4 mole fractions at Zhongshan reaches a minimum in February with a peak in September. Seasonal variation is closely connected with characteristics of seasonal change of CH4 source-sink, such as atmospheric circulation and source of vegetation in Antarctica. The annual average concentration and the growth rate of Antarctic stations are consistent, their annual amplitudes are all within the range of 1739-1767 ppb.There are some fluctuations with continuous and lower values in the Time-Series of daily average CH4 concentrations. In combination with the NCAR/NCEP reanalysis data during the same period, we speculate that the lower values are related to the atmospheric circulation. The air masses with lower CH4 content was delivered to the stations by cyclones, causing the decline in the concentration of CH4 at Zhongshan station.The monthly amplitude of CH4 concentrations at Zhongshan station is obviously higher in summer, there is an evident wavelike process in the Time-Series of daily average CH4 concentrations at Zhongshan station and South Pole station. What’s more, the obvious fluctuating phenomenon also exists at Syowa station. After analysis, we found that the fluctuation is irregular.