The background atmospheric concentrations of cyclic perfluorocarbon tracers determined by negative ion-chemical ionization mass spectrometry

The background atmospheric mixing ratios for a range of cyclic perfluorocarbons (cyclic-PFCs), widely used in atmospheric dispersion studies, have been measured by gas chromatography-mass spectrometry in negative ion-chemical ionization mode. Background concentrations range from <1 fl l−1 to >10 fl l−1, where femtolitre is expressed as parts in 1015 (ppqv). Because of their very long atmospheric lifetimes (>3000 yr) the present day concentrations represent the accumulated emissions from all sources, although significant commercial production did not commence until the 1960s. Cyclic-PFCs are potent greenhouse gases; however, their atmospheric concentrations are currently so low as to make an insignificant contribution to global warming.