The Long-distance Attraction Process Of Glyoxal In The Atmosphere And Its Influence Mechanism Of Reaction On The Aerosol Interface

Secondary organic aerosol（SOA）,a major component of the atmospheric particulate matter,profoundly impacts air quality,visibility and human health.Glyoxal（GL）is an important product of the photochemical oxidation of biogenic and anthropogenic VOCs with a global source of 45 Tg yr^-1.GL represents an important precursor of SOA,contributing a global SOA source of 2.6 Tg C yr^-1.Aqueous chemistry is a significant reaction pathway of GL for SOA formation.However,the aerosol interface has an essential effect on reaction mechanism of GL.The long-distance attraction mechanism of GL by aerosol and reaction mechanism of GL at the aerosol interface are uncertain.Thus,the classical molecular dynamics（MD）simulations and quantum chemical（QC）calculations are performed to explore the thermodynamic process of gaseous GL coming into the aerosol phase,reveal the the long-distance attraction mechanism of GL by aerosol,and clarify the hydration reaction mechanism of GL in the interior region of aerosol.Furthermore,the oligomerization reaction mechanism of GL at the aerosol interface is illuminated using QC calculation.The major conclusions are as follows:（1）The classical MD simulations show that GL is the most stable at the aerosol interface when gaseous GL undergoes the long-distance attraction,and the carbonyl O-atom of GL exhibits a preferential orientation to the aerosol interface.This indicates that the aerosol interface provides a stable reaction site for the atmospheric chemical reaction of GL.Simultaneously,t he uptake and accommodation abilities of aerosol interface to GL increase with the increasing acidity,contributing to the hydration reaction of GL at the acidic aerosol interface.When GL is in the interior region of acidic aerosol,hydration reaction barrier of GL(R_COM+SA)obviously decreases relative to the that of direct hydration reaction(R_GL+H2O)and indirect hydration reaction of GL with H₂O(R_COM+H2O)in the interior region of neutral aerosol.The rate constant of R_COM+SA is larger by 23 and 10 orders of magnitudeuptake of GL at the acidic aerosol interface.This contributes to oligomer formation of GL at the acidic aerosol interface.（2）When GL is adsorpted onto the aerosol interface,the direct hydration reaction of GL requires the activation barrier of 39.9 kcal mol^-1 and only releases reaction of GL is still barrierless and the reaction energy is up to-96.9 kcal mol^-1, interface is in favor of the protonation reaction of GL.The subsequent hydration and deprotonation reactions of cationic intermediate which is the product from protonation reaction of GL form diol（DL）and tetrol（TL）.The following protonation and dehydration reactions of DL and TL yield the first-generation carbenium ions(1^st-CB_s)which are lack of an electron.The positively charged C atom of 1^st-CB_sconducts the nucleophile reaction with the hydroxyl O atom of DL and TL,then undergoing the hydration and deprotonation reactions,leading to the alcohol dimers.The whole process is barrierless and exothermic.Similarly,the second-generation carbenium ions(2^nd-CB_s)from alcohol dimers reaction undergo the nucleophile reaction with DL/TL,then conducting the hydration and deprotonation reactions to form the alcohol trimers.Thus,the reactions between the continuous formed multi-generation carbenium ions and DL/TL can produce the multimers.Our results show that the aerosol interface has the long-distance attraction role in GL,which is in favor of GL staying at the aerosol interface,and subsequently conducts the polymerization reactions to form multimers.Thus,the influence of long-distance attraction process and interfacial chemistry on reaction mechanism of GL are required to consider when assessing SOA formation.Moreover,the oligomerization reaction mechanism of GL at the aerosol interface contributes to rapid formation of SOA in the atmosphere.The results also provide new idea for future research about the reaction mechanisms of other carbonyl compounds at the aerosol interface.