Physicochemical Properties And Toxicity Characteristics Of Liquid Phase Oxidation Products Of Phenolics

Secondary organic aerosol is the main component of atmospheric particulate matter,the source and formation mechanism of SOA are very complicated and received widespread attention.It have shown that aerosols generated through the liquid phase reaction path are important contributors to secondary organic aerosols.It have found that biomass combustion emissions can be used as important precursors of liquid secondary aerosols,but the key reaction parameters and their effects on the toxicity of SOA are insufficient.In this study,three phenolic compounds(resorcinol(RES),4-ethylphenol(4-EP)and 2,6-dimethoxy 4-methylphenol(DMP))which were from biomass combustion were selected as representative precursors for aqueous-phase oxidation with hydrogen peroxide(H₂O₂)in the presence or absence of light,using high performance liquid chromatography(HPLC),ultraviolet-visible spectrophotometer(UV-Vis),total organic carbon meter(TOC)and soot particle aerosol mass spectrometer(SP-AMS)to explore the reaction kinetics,yield,chemistry and light absorption properties of reaction products.This study detected the oxidation potential and cell survival rate of oxidation products with the aid of a spectrophotometer to reveal the effect of liquid-phase oxidation on the toxicity of particles.The main conclusions of this study are as follows:(1)In the aqueous-phase degradation reaction of biomass combustion emissions RES,4-EP,and DMP,0.10 m M precursor and 0.1 m M hydrogen peroxide had the fastest degradation rate under simulated visible light irradiation.It took 61 h,99 h and 104 h for the precursor concentration to degrade from 0.1 m M to 0.05 m M,respectively.4-EP and DMP may generate triplet excited state through light irradiation and oxidate themselves.Under the experimental conditions of this study,the pseudo first-order reaction rate constants of RES,4-EP,and DMP are 0.01130 h^-1,0.00696 h^-1 and 0.00666 h^-1,respectively.(2)In the aqueous-phase oxidation of res,4-ep and DMP,the absorbance of the solution system in the range of 300-600 nm showed an increasing trend with the reaction going on,and the absorbance of the liquid phase oxygen reaction in the presence of hydrogen peroxide and light increased most significantly.The results indicate that the liquid-phase oxidation process of the precursor forms substances with stronger light absorption characteristics,which indicates that the aqueous-phase oxidation process may affect the atmospheric radiation balance of the particles.(3)The aqueous-phase photooxidation of RES,4-EP,and DMP generated more products with larger ratio of mass-to-charge at the initial stage,but the proportion of ion fragments with correspondingly ratio of larger mass to charge(m/z)decreased with the increase of oxidation time.The proportions of ions with m/z 28(CO⁺)and m/z 44(CO₂⁺)increased with the increase of reaction time.This result indicates that polymerization occurred at the beginning of the reaction,but the fragmentation reaction process that occurred in the later stage of ring opening gradually became dominant.The hydrogen-to-carbon ratio(H/C)and oxygen-to-carbon ratio(O/C)of the product tended to change along a diagonal line with a slope of-1,indicating that the formation of carboxylic acid groups may be one of the main paths of the aqueous-phase oxidation reaction.(4)The biological toxicity test showed that the cell survival rate was significantly affected by the degree of oxidation.the toxicity of oxidation solution increased with the progress of aqueous-phase reaction.The change of oxidation potential was measured by the dithiothreitol(DTT)method.Compared with the starting point,the terminal oxidation potential increased,indicating that the secondary products of aqueous-phase oxidation may be the main reason for the possible change of oxidation potential.