Micro-FTIR Observation The Heterogeneous Reaction Of SO₂ Formation Of Sulfate

Sulfate(SO₄^2-)is one of the important constituent in atmosphere aerosols.But mechanisms of sulfate formation and the reaction kinetics have not been fully understood yet.Carrying out the heterogeneous reactions of sulfate formation can deepen our understanding of the mechanism of sulfate formation and also provide the necessary basis for the haze controlling in China.In this paper,the heterogeneous reactions of trace gas SO₂/O₃/NO₂onα-Al₂O₃ particles and MnCl₂ single droplets interface were investigated using microscopic Fourier transform infrared（micro-FTIR）technology.The intermediate transformation processes and reaction mechanisms were obtained.Moreover,we highlighted the reaction kinetics under different relative humidity（RH）,which supplied basic data for atmospheric chemistry modeling studies.（1）The heterogeneous reaction of SO₂/O₃ withα-Al₂O₃ particles as a function of RHs was investigated.The reaction products of SO₂ oxidation onα-Al₂O₃ particles in the presence or absence O₃ were obtained.And the reaction mechanism was speculated by infrared spectrum.The reaction rates and the uptake coefficient（γ）were obtained by the peak area of sulfate at different relative humidity.When O₃and SO₂ existed simultaneously during the reaction,the reaction rates enhanced by an order of magnitude as the RH increased from～15%to 95%,and the uptake coefficients increased 7-fold from 3.66×10^-7 to2.42×10^-6.The reason why the kinetic parameters were influenced by RH was given.（2）The heterogeneous reaction of SO₂/NO₂ withα-Al₂O₃ particles as a function of RHs was investigated.Firstly,the heterogeneous reactions of NO₂ withα-Al₂O₃ particles under different humidity（12%-86%）were investigated.During the reaction,the intermediate product of nitrite was observed.The different types of nitrates absorption peaks and the reaction mechanism were speculated by infrared spectrum.We highlighted the reaction of SO₂and NO₂simultaneously introduced to theα-Al₂O₃particles as a function of RHs（15%-90%）.The formation of nitrate species and intermediate products of N₂O₄ were clearly observed in the low humidity conditions.When RH increased above50%,there is no significant intermediate product of N₂O₄ and nitrate.According to the change of spectra,the reaction mechanisms under high and low humidity were speculated respectively.The kinetic parameters under different humidity were obtained,and the uptake coefficients increased from 4.20×10^-8 to 5.95×10^-7 as the RH increased from～15% to 90%.（3）The heterogeneous reaction of SO₂/O₃ with micron-sized MnCl₂ single droplets was preliminary investigated.The reaction rates were exhibited obvious sizes dependence.The reaction rate decreased with increasing droplet size.