Reaction Of Gas-phase Polycyclic Aromatic Hydrocarbons And C₆-C₁₀ N-alkanes Initiated By OH Radicals

Polycyclic aromatic hydrocarbons?PAHs?are semi-volatile organic compounds containing two or more benzene rings.They are ubiquitous highly toxic hazardous pollutants detected extensively in urban atmosphere.PAHs have been extensively studied because of their confirmed teratogenicity and carcinogenicity.They are by-products of incomplete combustion of fossil fuels and biomass.They have a certain activity in the atmosphere and are easy to react with atmospheric oxidants such as OH,NO₃ and O₃.It may produce more toxic oxygenated PAHs?OPAHs?and nitrated PAHs?NPAHs?,which are also mutagenic and carcinogenic and persist in the atmosphere.ANT and PHE are tricyclic aromatic hydrocarbons.There had several theoretical studies on oxidation of ANT and PHE initiated by OH radicals.Therefore,we attempt to obtain various possible transition states,branch ratio,final products and effective rate constants by coupling the quantum chemistry and kinetic calculations,and identify their major degradation pathways in the atmosphere.Organic nitrates refer to esters with nitric acid group and their derivatives,including peroxy nitrates?RO₂NO₂?and alkyl nitrates?RONO₂?.The RONO₂ studied in this paper are products of photochemical oxidation of VOCs with OH and NO₃ radicals in the presence of NO_x.The main results are as follows:?1?Atmospheric Oxidation of Anthracene and Phenanthrene Initiated by OH RadicalsThe oxidation starts by forming PAH-OH adducts which then react with O₂ and NO₂ in the atmosphere.Reactions of PAH-OH and O₂ start mainly by reversible O₂ addition,forming PAH-OH-OO radicals,which then undergo backward decomposition to PAH-OH+O₂,forward unimolecular isomerization to OPAHs products,and bimolecular reaction with NO.This calculation present all possible transition states as well as reaction paths,final products and effective rate constants.Calculations at both M06-2X and ROCBS-QB3 levels show that reaction of ANT with OH forms AR9 predominantly,followed by AR1;while reaction of PHE forms PR10,PR4,and PR1 in comparable amounts.The predicted branching ratios agree with a previous theoretical study for both ANT and PHE at DFT-BB1K level.O₂ adds to C10 of AR9 almost exclusively,forming AR9-10-OO,and then the only sensible channel is the intramolecular H-shift in AR9-10-OO.O₂ can add to C2 and C4 positions of AR1,forming AR1-4-OO and AR1-2-OO,and then AR1-4-OO would decompose back rapidly to AR1+O₂,while AR1-2-OO will cyclize to AR1-2,11-OO.AR1-2,11-OO can further break the bridged O-O bond to AR1-2O-9,11-O,and further barrierless cyclization to AR1-2,3-O-9,11-O.O₂ adds to C1 of AR2 almost exclusively,forming AR2-1-OO-s,which then cyclizes to AR2-1,3-OO-s.O₂ adds to C10 of PR9 almost exclusively,forming PR9-10-OO,and for PR10-9-OO,the only sensible unimolecular routes are the intramolecular H-shift resulting in formation of 2,2'-diformyl biphenyl.O₂ would add only to C1 and C3 sites of PR4,which will form PR4-1-OO and PR4-3-OO,and only PR4-3-OO can be irreversibly cyclize to PR4-3,12-OO.The only significant pathway for removal of PR1 proceeds via PR1-2-OO-s,which then cyclizes to PR1-2,11-OO-s?2?Experimental investigation of the reaction C₆-C₁₀ n-alkanes with OH radicals in the presence of NO_xIn this paper,we study the reaction of NO and RO₂ radicals generated in the reaction of C₆-C₁₀ n-alkanes with OH radicals,and try to detect the yield of RONO₂ generated in the reaction.The concentration of NO and NO₂ before reaction and the concentration of NO and NO₂+RONO₂ after reaction are measured by NO/NO₂/NO_x analyzer.Because both NO₂ and RONO₂ are displayed as NO₂ on the NO/NO₂/NO_x analyzer,the sample is photodegraded with395-405 nm UV LED strip to eliminate NO₂ before entering the analyzer,so as to distinguish NO₂ and RONO₂.It is found that 395-405 nm UV LED strip can photolysis pure NO₂,with a conversion of 56.1%;however,the photolysis of VOC+OH+NO_x reaction mixture doesn't reveal the change in concentration of NO₂+RONO₂,which needs further study.