(Research Center for Eco-Environment Sciences, Chinese Academy of Sciences, Beijing, 100085) A method to analyze trace hydrocarbons in the air by GC-PID is introduced. The constructive and working principle are described. Both of specifications of the instrument and the analysis results are given. The reliability of the results is analyzed. 1 Introduction Up today, the major methods to determine trace hydrocarbon gases in the air are by GC-FID and GC-MS. Due to the limit of sensitivity of the analysis methods, these compounds in the air must be pre-concentrated or enriched. Therefore, the complicated manipulation is needed, and wastes time too, and results in determination error. Especially, when the research for finding out the pattern of migration and change of these compounds in the air is required, the traditional analysis methods are getting more and more difficult. It is necessary to set up a sort of methods to determine trace hydrocarbons in the air, which should be fast and sensitive enough. Instead of GC-FID, a GC-PID has been constructed in the laboratory, and the trace n-Butane、n-Butylene、1.3-Butadiene and Isoprene in the air have been determined directly without any pre-concentration or enrichment. ..... download the file,from the link url.at this page top