Atmospheric Chemistry of Dimethyl Carbonate:  Reaction with OH Radicals, UV Spectra of CH₃OC(O)OCH₂ and CH₃OC(O)OCH₂O₂ Radicals, Reactions of CH₃OC(O)OCH₂O₂ with NO and NO₂, and Fate of CH₃OC(O)OCH₂O Radicals

Abstract

A flash photolysis-resonance fluorescence technique was used to study the rate constant for the reaction of OH radicals with dimethyl carbonate over the temperature range 252-370 K. The rate constant exhibited a weak temperature dependence, increasing at both low and high temperature from a minimum value of approximately 3.1 × 10 -13 cm 3 molecule -1 s -1 near room temperature. Pulse radiolysis/transient UV absorption techniques were used to study the ultraviolet absorption spectra and kinetics of CH 3 OC(O)OCH 2 and CH 3 OC(O)CH 2 O 2 radicals at 296 K. Absorption cross sections of CH 3 OC(O)OCH 2 and CH 3 OC(O)OCH 2 O 2 at 250 nm were (3.16 ( 0.34) × 10 -18 and (3.04 ( 0.43) × 10 -18 cm 2 molecule -1 , respectively. Rate constants measured for the self-reactions of CH 3 OC(O)OCH 2 and CH 3 OC(O)OCH 2 O 2 radicals and reactions of CH 3 OC(O)OCH 2 O 2 radicals with NO and NO 2 were (5.6 ( 1.1) × 10 -11 , (1.27 ( 0.21) × 10 -11 , (1.2 ( 0.2) × 10 -11 , and (1.2 ( 0.2) × 10 -11 cm 3 molecule -1 s -1 , respectively. The rate constant for reaction of F atoms with dimethyl carbonate was determined by a pulse radiolysis absolute rate technique to be (6.1 ( 0.9) × 10 -11 cm 3 molecule -1 s -1 . A FTIR smog chamber system was used to show that, in 760 Torr of air at 296 K, CH 3 OC(O)OCH 2 O radicals are lost via three competing processes: 42 ( 15% via reaction with O 2 , 14 ( 2% via H atom elimination, and 44 ( 10% via decomposition and/or isomerization. Relative rate techniques were used to measure rate constants for the reactions of F atoms with CH 3 OC(O)OCH 3 , (6.4 ( 1.4) × 10 -11 cm 3 molecule -1 s -1 , and Cl atoms with CH 3 OC(O)OCH 3 , CH 3 OC(O)OCH 2 Cl, CH 3 OC(O)-OCHO, and HC(O)OC(O)OCHO, (2.3 ( 0.8) × 10 -12 , (4.6 ( 2.8) × 10 -13 , (1.7 ( 0.1) × 10 -13 , and (1.7 ( 0.1) × 10 -14 cm 3 molecule -1 s -1 , respectively. Results are discussed in the context of the atmospheric chemistry of CH 3 OC(O)OCH 3 .

Atmospheric Chemistry of HFE-7100 (C4F9OCH3): Reaction with OH Radicals, UV Spectra and Kinetic Data for C4F9OCH2· and C4F9OCH2O2· Radicals, and the Atmospheric Fate of C4F9OCH2O· Radicals

“…On the basis of σ 260nm (CH 3 O 2 ) ) 3.18 × 10 -18 cm 2 molecule -1 9 the F atom yield at full radiolysis dose and 1000 mbar SF 6 was determined to be (3.18 ( 0.32) × 10 15 cm -3 . 8 The quoted uncertainty reflects both statistical uncertainties associated with the calibration procedure and a 10% uncertainty in σ(CH 3 O 2 ). 9 Reagents used were 0-27 mbar O 2 (ultrahigh purity), 950-1000 mbar SF 6 ,(99.9%), 0-19 mbar C 4 F 9 OCH 3 (>99%), 0-0.95 mbar NO (>99.8%), 0-1.3 mbar NO 2 (>98%), and 0-10 mbar CH 4 , (>99%).…”

A study of dimethyl carbonate conversion and its impact to minimize soot and NO emissions

“…In 1997, Bilde et al [13] investigated the atmospheric chemistry of DMC in the 252-370 K temperature range by using flash photolysis-resonance fluorescence techniques, to address the environmental impact of DMC in the case that it is released into the atmosphere. The authors concluded that, under these conditions, the reactivity of DMC toward OH radicals is low and is comparable to that of ethane.…”

Kinetics and mechanism of the OH-radical and Cl-atom oxidation of propylene carbonate

“…The product study indicates that the main product of the atmospheric photooxidation of propylene carbonate will be acetyl formyl carbonate which does not appear to be particularly stable. Reaction of acetyl formyl carbonate with OH radicals will be very slow and since neither the carbonate nor anhydride entities in its structure absorb in the tropospheric solar actinic region (l > 290 nm) 32,33 photolysis loss will also be negligible. Deposition on surfaces with formation of acetic and formic acids will probably constitute the main atmospheric fate of acetyl formyl anhydride.…”