Monthly Atmospheric CO2 Mixing Ratios from the NOAA CMDL Carbon Cycle Cooperative Global Air Sampling Network, 1968-2002

Starting in 1968, air samples were collected in cylindrical glass flasks tapered at both ends to ground glass stopcocks lubricated with hydrocarbon grease. At several sites from 1980 to 1985 samples were also collected in spherical 5-L flasks equipped with a single ground glass stopcock. These flasks were filled by the evacuation method described below. In 1983, measurements of CH4 in the flask samples were begun. Experiments at this time revealed that CO mixing ratios increased with time in the greased flasks. In 1989, 0.5-L glass flasks equipped with glass piston Teflon O-ring stopcocks were introduced into the network so CO could be measured in addition to CO2 and CH4. In 1990, measurements of 13C/12C and 18O/16O of CO2 in the flask samples were begun. The precision of the isotopic measurements was better with larger volume flasks, so in 1991 2.5-L glass flasks with two Teflon O-ring stopcocks began to replace the 0.5-L flasks. In 1994, the conversion of the network to 2.5-L flasks was completed. Samples continue to be collected in 2.5-L flasks.自1968年起，研究人员采用两端收窄并连接涂有烃类润滑剂的磨口玻璃活塞的圆柱形玻璃烧瓶采集空气样本。1980年至1985年间，多个站点同时使用配备单个磨口玻璃活塞的5升球形烧瓶开展样本采集工作，此类烧瓶通过下文所述的抽真空法完成充装。1983年，启动对烧瓶样本中甲烷（CH₄）的测量工作；同期实验发现，涂有润滑剂的烧瓶内一氧化碳（CO）的混合比随时间推移出现升高。1989年，该采样网络引入配备玻璃活塞-聚四氟乙烯（Teflon）O形圈活塞的0.5升玻璃烧瓶，使得除二氧化碳（CO₂）与甲烷外，一氧化碳的测量也得以实现。1990年，启动对烧瓶样本中二氧化碳的碳同位素比值（¹³C/¹²C）与氧同位素比值（¹⁸O/¹⁶O）的测量工作。由于更大容积的烧瓶具备更优的同位素测量精度，1991年起，配备两个聚四氟乙烯（Teflon）O形圈活塞的2.5升玻璃烧瓶开始逐步替代0.5升烧瓶。1994年，该采样网络完成向2.5升烧瓶的全面转换，目前仍沿用该规格烧瓶进行样本采集。