Calculation Simulation Of Sulfate Formation Mechanism On The Mineral Oxides Surface In The Atmosphere

Based on the atmospheric pollution in Sichuan Basin,aiming at the source and formation of sulfate aerosol particles,combined with the spatiotemporal variation characteristics of particles and monitoring pollutant concentration in the basin,this thesis established the reaction system of inorganic(H₂O₂and HONO)and organic(isoprene and limonene)on the mineral oxides(?-Al₂O₃and?-Fe₂O₃)surface.Adsorption mechanism of H₂O₂,HONO,isoprene and limonene on?-Al₂O₃and?-Fe₂O₃surface and heterogeneous oxidation mechanism of SO₂were studied,which are elucidated by analyzing the orbital hybridization,electron transfer and transition state.The main contents and conclusions include the following aspects:(1)Heterogeneous oxidation mechanism of SO₂by H₂O₂/HONO on?-Al₂O₃and?-Fe₂O₃surface:The adsorption and decomposition processes of H₂O₂/HONO on perfect and oxygen-defected(O_defect)?-Al₂O₃(Al)(110)and?-Fe₂O₃(Fe)(001)surface were analyzed by simulation,and the heterogeneous reaction mechanism of H₂O₂/HONO oxidation of SO₂on?-Al₂O₃and?-Fe₂O₃surfaces was revealed by experiments.The results show that the presence of H₂O₂/HONO not only increases the adsorption capacity of SO₂,but also promotes the transformation of SO₂to sulfate,and HONO can promote the formation of sulfate more than H₂O₂.The reason is that H₂O₂decomposes(H₂O₂?OH+OH)only on O_defect?-Al₂O₃(Al)(110)and?-Fe₂O₃(Fe)(001)surfaces to form hydroxyl radicals,while HONO decomposes(HONO?ON+OH)not only on prefect?-Fe₂O₃(Fe)(001)surface,but also on O_defect?-Al₂O₃(Al)(110)and?-Fe₂O₃(Fe)(001)to form OH radicals.Moreover,when H₂O₂/HONO and SO₂are co-adsorbed on?-Al₂O₃(Al)(110)and?-Fe₂O₃(Fe)(001)surface,SO₂was oxidized by OH radicals formed by the decomposition of H₂O₂/HONO on the surface to form sulfate,resulting in HONO+SO₂system(?-Al₂O₃:15.632 ppm;?-Fe₂O₃:19.675 ppm)compared with H₂O₂+SO₂system(?-Al₂O₃:5.432 ppm;?-Fe₂O₃:8.642 ppm)has a higher concentration of sulfate formation.Meanwhile,the calculation of the chemical reaction barrier of the decomposition process of H₂O₂/HONO and the oxidation process of SO₂by H₂O₂/HONO shows that SO₂is easily oxidized by H₂O₂/HONO on O_defect?-Al₂O₃(Al)(110)and?-Fe₂O₃(Fe)(001)surface to form sulfate.(2)Heterogeneous oxidation mechanism of SO₂by isoprene/limonene and ozone on?-Al₂O₃and?-Fe₂O₃surface:The co-adsorption mechanism of isoprene/limonene,ozone and SO₂,the formation and decomposition mechanism of Criegee intermediates(CIs)and the heterogeneous oxidation mechanism of SO₂by CIs were studied.Isoprene/limonene can not only promote the formation of sulfate on?-Al₂O₃and?-Fe₂O₃surface,but also form secondary organic aerosol(carbonyl compound).Limonene is easier to form sulfate and carbon compounds than isoprene.The process of ozone oxidation-decomposition of isoprene/limonene,the co-oxidation reaction of SO₂by isoprene/limonene and ozone on?-Al₂O₃(Al)(110)and?-Fe₂O₃(Fe)(001)surface includes four steps:the addition reaction of ozone and C=C of isoprene/limonene,the formation of CIs,the formation of defective oxygen(or the oxidation of SO₂by defective oxygen)and the formation of OH radical(or the oxidation of SO₂by OH radical).Among them,ozone tends to form CIs with CH₂=CCH₃-CH-O-O*structure by addition with C₁=C₂of isoprene on?-Al₂O₃(Al)(110)and?-Fe₂O₃(Fe)(001)surface,and OH radicals are formed by hydrogen transfer process to oxidize SO₂to form HOSO₂clusters and carbonyl compounds.Moreover,the surface adsorbed water can inhibit the oxidation of SO₂by isoprene and ozone by influencing the addition reaction and the formation of defective oxygen and OH radicals from the decomposition of CIs,thus reducing the sulfate content on?-Al₂O₃and?-Fe₂O₃surfaces(?-Al₂O₃:1.24 ppm?0.68 ppm;?-Fe₂O₃:3.24 ppm?1.83 ppm).However,for limonene,ozone tends to add with C₃=C₄of limonene to form CIs with R₃CHCH₃-O-O*structure.Compared with the process of oxidation of SO₂by defective oxygen(R₃CHCH₃-O-O*+SO₂?R₃CHCH₃=O+SO₃),R₃CHCH₃-O-O*intermediate is more inclined to obtain H atom from-CH₃group(R₃CHCH₃-O-O*?R₃CHCH₂-O-OH)to form OH radical,and oxidize SO₂to form HOSO₂clusters(R₃CHCH₂-O-OH+SO₂?R₃CHCH₂=O+HOSO₂).By enhancing the Al-3p/Fe-3d-C-2p p/d-p and C-2p-O-2p p-p orbital hybridization,the surface adsorbed water reduces the reaction barrier of addition reaction and decomposition of CIs to form OH radicals,and promotes the oxidation of SO₂on the surface of?-Al₂O₃(Al)(110)and?-Fe₂O₃(Fe)(001)by limonene and ozone.which makes the sulfate content on?-Al₂O₃and?-Fe₂O₃surface increase(?-Al₂O₃:0.63 ppm?1.68 ppm;?-Fe₂O₃:3.63 ppm?6.89 ppm).Therefore,limonene has higher sulfate concentration on the surface of?-Al₂O₃and?-Fe₂O₃than isoprene.The results not only better explain the heterogeneous reaction mechanism of isoprene/limonene and ozone oxidizing SO₂on?-Al₂O₃and?-Fe₂O₃surface,but also explain the inhibition and promotion of relative humidity on the process of isoprene/limonene and ozone oxidizing SO₂to sulfate.