Photolysis Of Selected Polycyclic Aromatics Hydrocarbons In Simulated Atmospheric Condensed Water

Polycyclic aromatic hydrocarbons(PAHs)are a kind of semi-volatile organic pollutants,PAHs in atmosphere mainly come from incomplete combustion of fossil fuel and biomass,and exist in the form of gas and particle phases.Direct photolysis is an important way to remove PAHs in the atmosphere because of the strong UV absorption ability of PAHs.When aerosol particles adsorbed PAHs appear in a high humidity environment,the particles will wrap water molecular layer or water film around aerosol particles,forming the atmospheric condensed water.The photolysis behavior of PAHs in the atmospheric condensed water is obviously different from that in the particle phase,because of the high concentration of water-soluble organic matter and inorganic matter.Study the photolysis behavior of PAHs in the simulated atmospheric condensate environment is helpful to improve the understanding of PAHs behavior in the atmospheric condensate water and provide reference for the simulation of PAHs atmospheric environmental behavior.Anthracene(Ant),phenanthrene(Phe)and pyrene(Pyr)are low molecular weight PAHs.Their solubility is 1.000,0.045 and 0.130 mg/L respectively.They are significantly affected by light.In this study,I choose Ant,Phe and Pyr as model compounds,and use a rotatable illumination device equipping with a 300W high pressure mercury lamp to simulate sunlight for 30 minutes.The effects of environmental coexistent components on the photodegradation of Ant,Phe and Pyr in the atmospheric liquid environment were comparatively studied by adjusting the acidity and Fe3+ concentration of the simulated condensate system.The conclusions are as follows:1.Ant,Phe and Pyr can photodegrade directly under UV irradiation.The photolysis rate constant of Ant is the highest,followed by Phe and Pyr,1.8404 min-1,0.1548 min1 and 0.1037 min-1,respectively.The photolysis of Phe and Pyr obeys the first-order kinetic equation,while the photolysis kinetic curve of Ant in water divided into two distinct stages.2.Hydrochloric acid was used to adjust the pH of the simulated system to 2 and 4.Compared with the control group(pH=6.5),the acidity could affect the photodegradation rate of Ant,Phe and Pyr.The enhanced acidity can significantly accelerate the photodegradation of Pyr and inhibit the photodegradation of Ant and Phe,but the photodegradation kinetic curves of Ant,Phe and Pyr were similar to the control group.3.When the pH value is adjusted to 2 and 4 using hydrochloric acid,Fe3+ provided by FeCl3 can form Photo-Fenton system in water to accelerate the photolysis of Ant,Phe and Pyr,and the stronger the acidity is,the stronger of Fenton system to PAHs is.Compared with the pure water group without Fe3+ in the same acidity,the photolysis rates of Phe and Pyr in Fenton system at pH=2 were increased by 75%and 55%,respectively,and the photolysis rates of Ant in the second stage increased by 115%.There is a linear relationship between the concentration of Fe3+ and the photolysis rate constants of Phe and Pyr in the simulation system,but the photolysis rate constant of Ant increased first and decreased later.Oxalic acid can inhibit the photolysis of Ant and Phe but promote the photolysis of Pyr.Ferrioxalate can only promote the photolysis of Phe.4.Collecting the PM2.5 samples in Xiamen.Using the extracting water of PM2.5 to simulate the effect of Water Soluble Organic Carbon(WSOC)with different concentrations on the photolysis of PAHs.With the increase of the concentration of water-soluble components,the photodegradation rate of Ant and Phe decreased linearly.The effect of water-soluble components on the photodegradation rate of Pyr was small,and the increase of concentration could slightly accelerate the photodegradation of Pyr.The water-soluble components of PM2.5 contain higher concentrations of unsaturated aldehydes and brown carbon,and that is just one of which affecting the photolysis of PAHs in the atmospheric liquid environment.Building Fenton system in simulated atmospheric liquid environment,the results show that Fe3+ can also accelerate the photolysis of PAHs,but the promoting effect is weaker than that of Fenton system in pure water.It is speculated that the existence of WSOC in PM2.5 weakens the photocatalytic effect of Fe3+.5.The simultaneous measurement of 9,10-phenanthrenequinone and 1hydroxypyrene produced in the photolysis process shows that 9,10phenanthrenequinone can also photolysis under UV irradiation.WSOC in PM2.5 can slow down the photolysis of 9,10-phenanthrenequinone,but 1-hydroxypyrene was not detected.6.Comprehensive analysis shows that the increase of acidity and WSOC concentration in the simulated atmospheric condensate water can accelerate the photolysis of Pyr,but inhibit the photolysis of Ant and Phe.Its environmental significance shows that in the process of fog droplet aging,with the evaporation of water,the increase of acidity and WSOC concentration in the condensate phase,the increase of atmospheric life of Ant and Phe,and the increase of environmental health risk.In addition,the photolysis of PAHs adsorbed on the aerosols containing iron can be accelerated by light Fenton reaction.Compared with carbon aerosols,the lifetime of PAHs adsorbed on the surface of dust aerosols is shorter.