The origins of individual organic pollutants in the atmosphere are of considerable interest, on the local scale for identifying pollution sources, and on the global scale because of potential effects on climate. Like many environmental pollutants the sources of chloroacetates are still not clearly identified. A method had been developed for quantifying biogenic contribution in environmental chloroacetates by radiocarbon analysis using off-line preparative capillary gas chromatography/ accelerator mass spectrometry (PCGC/AMS). 14C-Containing standards were synthesized. A method for isolation of chloroacetates from large-volume rain water and air samples and their preparation for PCGC separation was developed and optimized. Complete chromatographic resolution of the complex rain water extract can be achieved by two dimensional PCGC separation on two columns with different polarities, on a non-polar column, cryogenic trapping and further separation on a polar column gave pure chloroacetates. AMS-measurements of old and modern chloroacetate standards are done for calibration.