In-situ measurement of atmospheric CFC-11 at the Shangdianzi Global Atmosphere Watch (GAW) Regional Station

An in-situ GC-ECD system was used to measure halocarbons at Shangdianzi (SDZ) GAW regional station. In this paper, we reported observational results of atmospheric CFC-11 (CCl³F) mixing ratios from April 2007 to March 2008. The CFC-11 time series showed large variability. Approximately 62% observed values were filtered as non-background data. The median, 10% and 90% percentiles of CFC-11 background mixing ratios were 245.4 ppt (10^-12 mol/mol), 244.6 ppt and 246.1 ppt, respectively; whereas those of non-background CFC-11 mixing ratios were 254.7, 246.6 and 272.1 ppt, respectively. Significant differences in background and non-background CFC-11 mixing ratios were observed between summer and autumn, mainly because of the CFC-11 stored in foam being prone to atmospheric release in hot seasons. Comparison of the SDZ data with the five AGAGE stations suggested agreement with mid-high latitude Northern Hemisphere stations MHD, THD and RPB. The SDZ data were higher than that of Southern Hemisphere stations CGO and SMO. Higher CFC-11 mixing ratios measured in different seasons were always associated with winds from the W-WSW-SW sector, indicating that the airflow coming from this wind sector has a positive contribution to CFC-11concentrations. The CFC-11 mixing ratios were higher in autumn and summer than in spring and winter, in which its mixing ratios were very close to the atmospheric background level. This was happened especially when airflow originated from the NNE-NE-ENE-E sector, indicating the air masses coming from these wind directions was relatively clean.