Photo-induced Reactions Between HONO And Phthalate Esters Contaminants In The Atmospheric Aqueous

Phthalate esters?PAEs?are typical environmental endocrine disruptors.Since their large production and intractable biodegradability,PAEs become one of the most widespread pollutants,with enhanced trends of pollution.HONO is an important nitrogen-containing air pollutant that can undergo photolysis to produce·OH radicals,which largely determines the tropospheric oxidation capacity.Therefore,it is important to study the photochemical reaction of PAEs with HONO in atmospheric aqueous phase.In this paper,dimethyl phthalate?DMP?,diethyl phthalate?DEP?and dibutyl phthalate?DBP?were selected as the research objects.The effects of HONO concentration,pH and initial concentrations of PAEs on the photoreaction were investigated.The properties and kinetic characteristics of transient species were explored by 355 nm laser excitation,and the photochemical reaction mechanism was proposed.The conclusions were shown as following:?1?HONO concentration,initial DMP concentration and pH could all strongly affect the oxidation efficiency of DMP.The primary step of the reaction was mainly due to the attack of·OH radicals on aromatic ring to form DMP-OH adduct,and the bimolecular rate constant was determined as?5.5±0.4?×10⁹ L mol^-11 s^-1.The DMP-OH adduct could not only undergo monomolecular self-decay with a rate of?1.6±0.3?×10⁴s^-1but also interact with HONO,H₂ONO⁺and O₂ with rates of?6.4±0.4?×10⁶ L mol^-11 s^-1,?8.8±0.5?×10⁶ L mol^-11 s^-11 and?1.6±0.1?×10⁸ L mol^-11 s^-1,respectively.In addition,a small amount of·OH can attack the side chains to convert DMP to some dealkylated analogues.?2?Species-specific rate constants for reactions of DEP with HONO and NO₂^-were measured to be 0.049 and 0.0058 L mol^-1s^-1,respectively.Laser flash photolysis studies indicated·OH radicals originating from N?III?photolysis mainly attacked aromatic ring of DEP to produce DEP-OH adducts with a second-order rate constant of?4.2±0.1?×10⁹L mol^-1s^-1,while small amount of·OH could attack the side chain for hydrogen abstraction.DEP-OH adduct undergo several decay channels containing monomolecular decay,interaction with HONO and oxygen,and interaction with HONO would generate nitro-compounds.The possible transformation mechanisms of DEP were proposed.The atmospheric model showed that·OH radicals dominated the DEP removal pathway in the troposphere?3?Steady-state studies suggested the removal efficiency of DBP was strongly affected by pH,HONO concentration and bromide ions while showed insignificantly change in the variations of initial DBP concentration and chlorine ions.LFP experiments indicated that·OH-initiated reactions were crucial steps for photochemical reactions of DBP with HONO and two main pathways,·OH-addition and H-abstraction were proposed.The overall rate constants for the reaction of DBP with·OH were determined by competition kinetic methods to be 5.6×10⁹ L mol^-11 s^-1.Comparison the individual reaction rate constant for aromatic ring addition with the absolute rate constant implied the majority of the·OH radicals?69%?attacked the aromatic ring of DBP.The major transformation products were identified by GC-MS and the trends of their yields with time were given as well.These results provided critical insights into the photochemical transformation of DBP in real atmospheric environment.