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.

1968年起，空气样本采用两端渐缩至磨口玻璃旋塞（ground glass stopcocks）的圆柱形玻璃烧瓶收集，旋塞以烃类润滑脂润滑。1980至1985年间，部分站点还使用配有单个磨口玻璃旋塞的5升球形烧瓶采集样本；这些烧瓶通过下述抽真空法（evacuation method）填充。1983年，开始对烧瓶样本中的甲烷（CH4）进行测量；同期实验表明，涂有润滑脂的烧瓶中一氧化碳（CO）混合比随时间升高。1989年，配备玻璃活塞聚四氟乙烯（Teflon）O型圈旋塞的0.5升玻璃烧瓶被引入采样网络，从而可在测量二氧化碳（CO2）和甲烷之外，同时测量一氧化碳。1990年，开始对烧瓶样本中二氧化碳的碳-13/碳-12（13C/12C）及氧-18/氧-16（18O/16O）同位素比值进行测量。由于大体积烧瓶的同位素测量（isotopic measurements）精度更优，1991年起，配有两个聚四氟乙烯O型圈旋塞的2.5升玻璃烧瓶开始替代0.5升烧瓶；1994年，采样网络全面转换为2.5升烧瓶，此后样本采集均采用该规格烧瓶。