A study of four-year HCFC-22 and HCFC-142b in-situ measurements at the Shangdianzi regional background station in China

摘要

Atmospheric HCFC-22 (CHClF_2) and HCFC-142b (CH_3CClF_2) in-situ measurements have been recorded by an automated gas chromatograph-electron capture detectors (GC-ECDs) system and a gas chromatog-raphy/mass spectrometry (Medusa-GC/MS) system at the Global Atmosphere Watch (GAW) regional background station Shangdianzi (SDZ), China. The mixing ratios of the two HCFCs at SDZ show frequent events with elevated concentrations due to polluted air from urban or industrialized areas. The mean background mixing ratios for HCFC-22 and HCFC-142b were 205.3 ppt (parts per trillion, 10~(-12), molar) and 20.7 ppt, respectively, for the study period (March 2007-February 2011). The yearly background mixing ratios for the two HCFCs at SDZ are similar to those measured at Trinidad Head and Mace Head located in the Northern Hemisphere (NH), but larger than Cape Grim and Cape Matatula (located in the Southern Hemisphere) due to inter-hemispheric differences caused by predominantly NH emissions. During the study period, background mixing ratios exhibited positive growth rates of 8.7 ppt yr~(-1) for HCFC-22 and 0.95 ppt yr~(-1) for HCFC-142b. HCFC's seasonality exhibits a summer/autumn maximum and a winter minimum. 4-year averaged background seasonal amplitudes (maximum-minimum) are 6.0 ppt for HCFC-22 and 0.9 ppt for HCFC-142b. The seasonal fluctuations (maximum-minimum) in polluted events are 105.4 ppt for HCFC-22 and 29.1 ppt for HCFC-142b, which are much stronger than the fluctuations under background conditions. However, both HCFC-22 and HCFC-142b show summer minima in 2008, which is most likely due to emission control regulations when the Olympic Games were held in Beijing.