Dioxins arethegeneralterm for polychlorodibenzo-p-dioxins （PCDDs） and polychlorodibenzofurans （PCDFs）. Due to their properties of carcinogenesis， tetratogenesis and mutagenesis， and may enter human body through food chain and endanger the human health， PCDD/Fs have been enlisted in Stockholm Convention. The major sources of PCDD/Fs are waste incineration， chemical industry production， metal smelting and refining process， and paper manufacturing industry.The PCDD/Fs in the atmosphere are in the form of gas phase or particles， which are mainly influenced by saturated vapor pressure and temperature. At the ambient temperature， low chlorinated PCDD/Fs （mainly with six or less chlorine atoms） have high concentration in the gas phase， while high chlorinated PCDD/Fs （primarily hepta-and octa-chlorinated homologues） mainly distributed in the particle phase. In the flue gas， 82%-93% of PCDD/Fs are distributed in the gas phase due to high temperature. The atmospheric fate for PCDD/Fs is removed from the atmosphere via the dry or wet deposition， photolysis and the reactions with the atmospheric oxidants （including OH radical， HO2 radical， O3， NO3 radical， and Clatom）. Particle-phase PCDD/Fs are removed from the atmosphere via the dry or wet deposition， while gas-phase PCDD/Fs are depleted via photolysis and degradation reactions. It is critical to know the reaction mechanism and accurate rate coefficients of PCDD/Fs with various oxidants in order to assess their dominant atmospheric fate.
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