Theoretical Modeling On The Formation Mechanisms Of Secondary Organic Aerosols Via Substituted Aldehydes With Sulfuric Acid Assisted

The formation mechanisms of secondary organic aerosols with sulfuric acid assisted are investigated by quantum chemical methods and canonical transition state theory as follows:（1）Using M06-2X,CCSD（T）-F12a and traditional state theory with Eckart tunneling theory,the mechanism and kinetics of HFCO+H₂O reactions catalyzed by sulfuric acid and formic acid were studied.The effects of the above hydrolysis in the atmosphere were discussed.The calculated results show that sulfuric acid has a significant catalytic effect in the gas-phase hydrolysis of HFCO,and the reaction energy barriers are reduced from 39.22 and 41.19 kcal/mol to 0.26 and-0.63 kcal/mol,respectively.Sulfuric acid can further accelerate the decomposition of FCH（OH）₂ into hydrogen fluoride（HF）and formic acid（HCOOH）.However,after comparing the reaction rates,the analysis results show that the reaction of HFCO with OH radical is still the main pathway for the tropospheric degradation of HFCO.When the concentration of OH is about 10¹molecules cm^-3 or less in the atmosphere,the gas-phase hydrolysis of HFCO may occur catalyzed by sulfuric acid.Finally,it is emphasized that the HFCO+H₂O+H₂SO₄ reaction may occur more easily on the surface of the secondary organic aerosol（SOA）,thus participating in the formation of the secondary organic aerosol.（2）The mechanism of hydrolysis of trifluoroacetaldehyde（CF₃CHO）catalyzed by sulfuric acid and formic acid were studied by utilizing CCSD（T）-F12a/jun-cc-p V（Thald）Z//M06-2X/MG3S theoretical method.The importance of the above hydrolysis reaction in the atmosphere was discussed.Through the optimization of geometric structure,it can be obtained that when sulfuric acid is added as a catalyst in the hydrolysis reaction,a total of 16 transition states with different structures are produced due to the isomerization of sulfuric acid and the rotation of H atoms.In addition,sulfuric acid and formic acid as catalysts have remarkable catalytic effect on the reaction of CF₃CHO+H₂O.With the help of sulfuric acid,the energy barriers of CF₃CHO+H₂O reaction decreased from 32.98 kcal/mol and 33.52 kcal/mol to-8.97kcal/mol and-9.24 kcal/mol,respectively.It is worth noting that according to the calculation of the relative reaction rate,we found that the gas-phase hydrolysis of CF₃CHO catalyzed by sulfuric acid may compete with the reaction of CF₃CHO+OH when the concentration of OH decreases to 1×10⁴ molecules cm^-3,below 280 K at night.Therefore,the reaction of CF₃CHO+H₂O+H₂SO₄ may become a new way for the deposition of CF₃CHO in the atmosphere.We may find a new CF₃CHO sink reaction pathway in the atmospheric troposphere.