Distinct patterns found in ambient mixing ratios of atmospheric compounds in China

High precision measurements of three CFCs, three HCFCs, six HFCs, three PFCs, and SF6 were made at five Chinese background stations from January 2011 to December 2012. Their station means in the background air were comparable with those measured at the two AGAGE stations: Mace Head, Ireland and Trinidad Head, USA.

Compared with results for earlier years from in-situ measurement at SDZ, background-air mixing ratios of CFCs are now declining, while those for HCFCs, HFCs, PFCs, and SF6 are still increasing. The ratios of the number of sampling events in which measured mixing ratios were elevated above background (pollution events) relative to the total sample frequency (POL/SUM) for CFCs, HCFCs, and HFCs were found to be station dependent, generally LAN > SDZ > LFS > XGL > WLG.

The enhancement generally shows distinct patterns, with HCFCs> HFCs> CFCs> PFCs at five stations. Combining with the molecular weights, the biggest emissions of HCFCs in the regions around these Chinese sites compared to HFCs and CFCs, while the smallest of PFCs were consistent with CFCs being phased out and replaced with HCFCs in China.

In addition, relative emission strengths of these halocarbons in China were inferred as HCFC-22 > HCFC-141b > HFC-134a > HCFC-142b for the Yangtze River Delta (YRD) and as HCFC-22 > HCFC-142b > HCFC-141b z HFC-134a in the North China Plain (NCP).

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Ambient mixing ratios of atmospheric halogenated compounds at five background stations in China. Zhang, G., B. Yao, M.K. Vollmer, S.A. Montzka, J. Mühle, R.F. Weiss, S. O'Doherty, Y. Li, S. Fang, and S. Reimann (2017), Atmos. Environ., 160, 55-69 (doi: 10.1016/j.atmosenv.2017.04.017).